DC Universe

The DC Universe is a alternate reality of the Mortal Kombat universe where non of the Kombatants exist. Instead they have Super Heroes such as Superman and Super Villains such as Darkseid.

Zaterra

About Zaterra

Zaterra was home to Reptile's race of Saurians who originated fromEarthrealm long before it was annexed by Outworld through ten consecutive victories in Mortal Kombat. It used to be ruled by a matriarch. Her influence on the other members of the Saurian race is so strong that over time, they begin to revert back to a more primitive consciousness, the longer they are separated from her presence, which also affects their ability to maintain a humanoid appearance. In Mortal Kombat: Conquest, however, a former soldier of Reptile says that Zaterra wasn't destroyed becauseShao Kahn came to the realization that the Saurians would make wonderful allies in his plans.

In the television series Mortal Kombat: Conquest, Zaterra is depicted as very rainy; thunder can be heard along with the drenching rain, and many transparent Saurians crawl along the limbs of the trees.

It is unclear when Zaterra was conquered by Outworld, but Nitara's vampire people kept records of their existence before they were annexed by Outworld as well. The known Saurians also seem to retain no memories of their home world, which suggests that the conquest of Zaterra happened in a distant past. Though the Saurian people inhabited the realm prior to being conquered, their first home was Earthrealm which they were forced to leave during the catastrophic battles between Shinnok and Raiden.

A picture in Mortal Kombat: Deadly Alliance's krypt shows the three forms of Reptile in a very swampy area with a primitive-looking house built out of stone or possibly bone, indicating what the world may look like and that it has a clearly primitive technological level.

In an episode of Mortal Kombat: Defenders of the Realm, an item named "Gem of Tetsurri" is shown. It was revealed that it is not a gem but the crystallized heart of Zaterra's former king, Tetsurri.

Notable residents 

Because Zaterra is technically still a part of Outworld, it does not have any notable residents, but Reptile andKhameleon could qualify as Zaterrans since they belong to the Saurian race. It's also speculated that the Vampire race also hails from Zaterra, due to their apparently vast amount of knowledge about the Saurians, although this would pose an issue with Nitara's ending in Mortal Kombat Deadly Alliance, which has been shown to have, at least, partially occurred. It is also speculated that Chameleon hails from here. Kiri and Ankha are also two Saurians whom appeared in the series Mortal Kombat Conquest, While another Saurian named Komodaiappeaered in the cartoon series Mortal Kombat Defenders of the Realm

Void

History

Referenced as a mortal by-pass into the Heavens (the residence of the Elder Gods), the Void represents the "white space" of the universe, despite its actual appearance remaining unknown. Soulnados (passageways for souls of the deceased) are depicted as possible gateways into the Void, achievable through "breaking free" of the aggressive spirits within them and slipping into non-existence.

Vaeternus

Vaeternus was a realm that was conquered long ago by Shao Kahn and was incorporated within Outworld.

This dimension was home to the vampires and one of their kind, Nitara, sought a mysterious orb within Outworld which would permamently release her dimension from Outworld. She was successful in her goal and freed her homeworld through the aid of the cyborg ninja Cyrax.

Rellim ocanep

Rellim Ocanep is a realm from Mortal Kombat. It was never actually seen in-game, but was referenced in Mortal Kombat 3, Ultimate Mortal Kombat 3, and Mortal Kombat Trilogy upon winning 100 straight matches in two player mode. This feat bring the victorious player to a black screen claiming that they were entering the realm of Rellim Ocanep. This would then treat them to a game of Galaga.

While it has not yet been a canon part of the storyline, it was stated as a realm in-game and thus should be kept in mind when including a list of all Mortal Kombat realms.

Outworld

About Outworld

Outworld's known history goes back millions of years and points at Onaga the Dragon King, as its first ruler. Though he would eventually be supplanted by Shao Kahn, they both shared the same visions of expanding Outworld by taking other realms by force. Unwittingly, both were being controlled by the echos of the One Being. Outworld is an empire that stretches out over numerous realms which have been magically annexed. Despite the despotism both emperors have displayed, Outworld is in a constant state of turmoil, more so under Shao Kahn than it was under Onaga. Outworld is a large realm of varying landscapes. Outworld's primary landscapes appear to consist of, mostly barren wastelands, deserts, pools of acid, dense forests with animated faces, and high, mysterious mountain peaks. Small villages are scattered throughout the landscape, and like Edenia, the realm teems with magic. Beyond the imperial palace, the great temple of the Dragon King and the city of Lei Chen, no real metropolis seem to exist on Outworld. Outworld also houses a brewery, specializing in creating 'Outworld Wine,' popularly drank by master Bo' Rai Cho. It's often rumored amongst many Outworld inhabitants that Earthrealm's rice wine 'puts Outworld Wine to shame'. Commuters also ride the Dragonfly, said to be the fastest form of transportation across the vast expanses of Outworld, aside from sorcery. There are many of these flying transports, each with its own set of destinations.

Native realm species

Due to Outworld's composite structure, not all races found on Outworld are truly native to it, but some have been there for so long they have virtually become natives.

Originally native

Cryomancers. Though now extinct, they used to be a race that lived in Outworld long ago. They resemble very pale humans and have a natural affinity with ice. A few scattered descendants of this race live onEarthrealm (such as the ninjas Sub-Zero and Frost). It is unclear why their race died out.

Outworlders. Like most inhabitants of the realms of Mortal Kombat, Outworlders look like humans, but they seem to have a greater talent for magic and longer life expectancy. All Outworlders seen so far resemble East Asian people of Earthrealm. Though they dislike their rulers, each of them have their own schemes to attain more power and influence. There are only four known Outworlders, they are Li Mei, Bo' Rai Cho, Reiko, and Shao Kahn. 

Originally non-native or of uncertain origin

Shokan, described as "half-human, half-dragon," are a humanoid race appearing as abnormally tall and muscular, with four arms and skin patterns, with some being reminiscent of felines. They are organized in terms of a clan-based monarchy. They are fierce warriors and hate the Centaurs.

Centaurs/Centaurians. Though largely resembling the mythical creatures of Earthrealm with the same name, this breed is more vicious, with scorpion-like tails and horns. They are renowned hunters and seem to do so in packs. Centaurs have been the natural born enemies of the Shokan for ages.

Vampires have been a part of Outworld since their realm was annexed by Shao Kahn. They possess the ability to travel in between realms and are excellent record-keepers. Contrary to other fictional vampires, they can move by daylight, but are highly allergic to Earth's sun. The realm Vaeternus, from which the vampires originated from was freed in 10 AMK by Nitara.

Zaterrans are a virtually extinct, reptilian race that was once governed by a matriarchy on the realm ofZaterra, though even that world was not their first home. Despite their great talents as hunters, spies or messengers and their ability to become invisible, they are branded as untrustworthy slaves.

Tarkatans, also known as Mutants or Nomads, are a nomadic, humanoid race feared for their extreme bouts of rage and primitive lifestyle. Tarkatans are a breed of Netherrealm demons and Outworlders. They have spikes on their head and elbows, and retractable blades on their forearms. They also possess sharp fangs and are notorious cannibals. Though originating from the Netherrealm, at some point they emigrated to Outworld, where they have remained since.

Edenians, originally from the realm of Edenia, became inhabitants of Outworld after losing 10 consecutive Mortal Kombat tournaments against Shao Kahn's militia. Biologically similar to other humanoids, Edenians are rumoured to be descended from the Gods themselves, explaining their extremely long lifespans, slow ageing process and natural affinity with aerial magics. Although many returned to the liberated Edenia following the failed invasion of Earthrealm, some Edenians remained in Outworld, having no or few recollections of their homerealm and unable to forge affinity for the place. Edenia is ruled in a diarchy by Queen Sindel and her daughter Kitana, with loyal native Jade commanding the Royal Knights. Edenian traitors and defectors include Rain, Tanya and Daegon.

Native

Outworlder: Bo' Rai Cho, Li Mei, Reiko, Shao Kahn.

Saurian: Chameleon, Khameleon, Reptile. (Though originally from Zaterra.)

Shokan: Goro, Kintaro, Sheeva.

Tarkata: Baraka.

Centaurian: Motaro.

Other: Ermac, Onaga, Mileena.

Foreign

Hotaru (Seido)

Kano (Earthrealm)

Nitara (Vaeternus)

Quan Chi (Netherrealm)

Red Dragon (Earthrealm)

Shang Tsung (Earthrealm)

Shujinko (Earthrealm)

Special Forces (Earthrealm)

Locations

Armory

Dragon Mountain

Dragon King's Temple

Falling Cliffs

Golden Desert

Hell's Foundry

Kuatan Palace

Lei Chen

Living Forest

Lost Bridge

Lost Tomb

Lower Mines

Lumbermill

Makeba

Outworld Spire

Portal

Sea of Blood

Soul Tombs

Sun Do

Wasteland of Outworld

Cobalt Mines of Shokan

Orderrealm

About Orderrealm

As the polar opposite of Chaosrealm, Seido is a place where law, order and structure prevail above anything else. It appears to be a clear, advanced, highly urbanized and civilized world. In a geographical standpoint, Seido, the realm of Order appears to be nothing more than a highland made up of many narrow, bridge-like roads that rests upon on an unknown agent. Incredibly long trees appear to grow from the bottom of the roads, liquid water appears from fountains despite having no means of formation, and small streams of water flow into non-existence. This may explain, though not stated, that Seido may also have lowlands, or it may be be due to the realm's magical properties. As a result of its structure, many buildings rest upon narrow walkways, and the inhabitants are well-adapted, as none show any fear of falling. Seido is divided into various towns decided by color, such asBluetown, Greentown, Redtown and Goldtown. This does not merely apply to the road itself, but also to houses and huts in the area as well. Seido is also home to gemstones, such as the Green Gems, Gold Nuggets,Fire Opals, and Winterstones. Each gem shares the same color of the town they are located and vary in value and rarity. Because of Seido's strict policies, the realm is often at war.

Seido takes its name from the Japanese word seidō (制度) meaning a system or organization.

Due to a glitch in the game, if one were to try to walk off the edge of the road, in certain spots, they would walk on air and would be able to leave the map.

Native Realm Species

Thus far, the only known species inhabiting Orderrealm are Seidans. Seidans are humanoid in form, but like many other species in the realms of Mortal Kombat, possess greater affinities with magic and likely have a longer life expectancy. They are obsessed with structure and organization, which has lead to the fact they seem to care more about abstract things than they do about life and death, which makes them, curiously, a lot like the Chaosrealmers. Despite the egalitarian, clear outlook of their society, Seidans are tense people and many have reservations about their ruling caste, as is demonstrated by Darrius's Resistance movement. Many inhabitants are also well-adapted to the nature of their realm, as they often appear busy and/or rushing to their destinations. Despite the strict laws, some everyday citizens (excluding the Resistance) still commit serious crimes such as murder, though they never get away with their crimes.

Government 

According to the Seidan Guardsmen, freedom is disallowed because 'freedom leads to anarchy, anarchy leads to chaos, chaos leads to suffering.' As a result, Seido has innovated strict laws, making the realm safe, but difficult to reside. Though many Seidans feel safe in the realm of Seido, some believe the laws are too harsh, as Seido's citizens can face years of imprisonment for breaking a mere curfew, an offense considered minor by citizens of other realms, and even by some Seidan citizens. It is unknown whether or not Seido has a true ruler. In Darrius' ending in Mortal Kombat Deception, Shujinko mentions that a Seidan senate existed. This implies that Seido is a democratic realm, though nothing else is known about the Seidan government except for the Seidan Guard. The Seidan Guard is a group of warriors led by Hotaru enforcing the law by any means necessary, with their greatest enemy being the armed Resistance, an amalgamation of revolutionaries who are dissatisfied with the realm's strict policies, led by Darrius. The Resistance, with crude tactics, influences other oppressed Orderrealm inhabitants to join their cause to oppose the Seidan Guard. Despite being a safe realm, Seido is marked by a constant strife between the Seidan Guard and the armed Resistance, therefore resulting in many riots initiated by the Resistance. Both sides are equally ruthless and manipulative in their conflicts.

Notable Residents

Native

Dairou

Darrius

Hotaru

Relationships with other Realms

As long as the government can enforce order in a realm, the people of Seido will consider any realm an ally. Most other realms share an uncertain or uneasy relationship with the realm such as Edenia because of how suppressive the law enforcers of its realm can be towards maintaining order. Seido is allied with Outworld because the Seidan Guardsmen, more specifically leader Hotaru, ruled the walled city of Lei Chen to maintain outposts of law and order and to provide protection. Seido's biggest threat is received from its polar opposite, the Chaosrealm because of its primitive nature. They are at war with Chaosrealm for wanting to control their water, resulting in Chaosrealmers enacting riots. With other realms however, it fears no real threats, remaining a truly neutral realm.

Nexus

The Nexus is a fictional plane of existence in the Mortal Kombat video gameseries that exists as the central hub between the various realms of existence. The concept was first (and only) introduced in the game Mortal Kombat: Deception, as part of the game's Konquest mode.

History and Characteristic

According to the game, the Nexus was created by the Elder Gods to aid their chosen champion in his defense of the realms. The Nexus itself consists of a circular plane bordered by torch pillars that float amongst the clouds in an unknown place. It is rumored that the clouds are meant to suggest that it is located in the Heavens, being it that it was created by the Elder Gods, but such has not been confirmed by Midway Games. Present in the Nexus is an altar to the Elder Gods. Upon it are spaces to place each of the Kamidogu and the Amulet Of Shinnok). The only entrances/exits in the Nexus are a series of six portals, which only open when the appropriate Kamidogu are placed upon the altar. The portal to Earthrealm is available when the Earthrealm Kamidogu is obtained, and when the Earthrealm Kamidogu is placed on the altar, the Netherrealm is revealed. After the Kamidogu from the Netherrealm is obtained and placed on the altar, the Chaosrealm is opened. The Chaosrealm Kamidogu unlocks the Outworld, which in turn will unlock the Orderrealm and Edenia when the appropriate Kamidogu are obtained and placed on the altars. It is said in the game that when all 6 Kamidogu and the Amulet are placed on the altar, the Kamidogu will be transported to the presence of the Elder Gods. Unfortunately, in the video game, once all of the Kamidogu are collected, Onaga appears and steals them, preventing the player from discovering whether or not this is true. Onaga's words suggest that the Kamidogu would not be able to be transported to the Elder Gods unless one had the Amulet of Shinnok, which is not available for collecting during Konquest mode. It is suggested that only the Champion of the Elder Gods would be capable of accessing and utilizing the Nexus for easy transportation between the realms, but this is apparently not the case. As per Deception's storyline, Scorpion is deemed the true champion of the Elder Gods, but Shujinko, Monster, and Onaga all prove capable of entering the Nexus during Konquest mode.

The Nexus in MK: Deception

The Nexus is the central hub of travel in Mortal Kombat: Deception's Konquest mode. After Shujinko obtains the first Kamidogu, Damashi explains to him how to use it to access the portal in Earthrealm and how to get to the Nexus. Once Shujinko is in the Nexus, he places the Earthrealm Kamidogu on the altar, which unlocks the Netherrealm portal. Shujinko then travels sequentially to the Netherrealm, Chaosrealm, Outworld, Orderrealm, and Edenia, unlocking the portal to each level by obtaining the Kamidogu from the previous realm of existence. Once all of the Kamidogu have been collected, Onaga (the Dragon King) appears and steals them, marking the end of the mandatory portion of the quest. From there, Shujinko is still free to walk the realms to do as he sees fit, usually involving the player returning to realms to collect koins and unlockable items.

Kombat in the Nexus

The Nexus is also used in the game as a kombat arena. This occurs twice during the Konquest mode, and also as many times as the player sees fit after he or she unlocks the arena for the versus mode. It is worth noting that when kombat takes place in the Nexus, the altar and portals mysteriously disappear. The arena also has a suprise Death Trap, not expected by anyone prior to the game's release, that allows a player to knock the opponent through the wall surrounding the arena and into the swirling void beyond, never to be seen again.

Monster

After obtaining the second Kamidogu from the Netherrealm and placing it on the altar in the Nexus, an unknown character approaches Shujinko, claiming to be the true champion of the Elder Gods. Shujinko naturally takes offense, having been informed by Damashi that he is the real champion, and a fight breaks out between the two characters. Monster (revealed by name only through his life bar during Kombat) is really offenseless, but has the exact same moves as Scorpion, the other supposed true champion of the Elder Gods. After defeating Monster, Shujinko inquires of Damashi as to who he is, and Damashi responds that he doesn't know.

Scorpion

After having obtained the sixth Kamidogu, Shujinko returns to the Nexus in an attempt to place the final Kamidogu on the altar. Scorpion then appears in the Nexus, demanding that Shujinko stop interfering in the affairs of the Elder Gods. Shujinko and Scorpion then engage in Mortal Kombat in the final battle of Deception's Konquest Mode. After he is defeated, Scorpion disappears as well, and no further mention of his appearance is made in light of Shujinko turning his attention to the fact that his quest is finally complete.

Netherealm

The Netherealm (or Netherrealm) is a realm in the Mortal Kombat series. This place can also be considered as what we would call Hell in the Abrahamic faiths. It seems to resemble an eternal volcanic "continent," containing many volcanoes and lava pits.

About 
Shujinko: "This place... it feels dark."

Damashi: "As dark as every heart that inhabits it. Your presence here would not be possible. Only evil resides in this realm."

Netherealm appears to be, like Outworld, a realm composed of thousands of different layers. In the Mortal Kombat universe, deceased souls or entities who have committed major crimes descend into the Netherealm to undergo endless torture. In fact, one cannot enter the Netherealm without being evil or have a soul tainted with evil. It is an alternative, more generic name for the Abrahamic concept of Hell, as one of its former rulers was Lucifer (whose name appears only in the Sub-Zero game manual but not in-game). It is also described as "the darkest region of reality", and is inhabited by demons, monsters, and beings of the purest evil.
Though exits from and entrances to the Netherealm are very limited for obvious reasons, the world had quite a tumultuous history. Millions of years ago, the fallen Elder God Shinnok was banished there. After ages of imprisonment, he was able to break free, deposing Lucifer in the process. He restructured the realm to bear some resemblance to Earthrealm, the world which he had long desired to make his own. He later used it as a staging ground for the invasion of Edenia, but found himself cast into the depths of the realm again after this invasion was foiled. The abandoned war machines of Shinnok were then put to good use by one of his former acolytes, Noob Saibot.
Two locations within this realm include the Bridge of Immortality and the Prison of Souls. These are almost like the Di Yu in Chinese Mythology. The Prison of Souls is the Chamber of Grinding and so is the Slaughterhouse. Shinnok's Spire resembles that of Yan Wang's spire in 'Journey to the West.'
In Mortal Kombat: Deception's Konquest mode, Shujinko arrives during the "Festival of Torture", in which dead bodies burn and inhabitants watch them.

Native realm species
In a generic sense, many demons and spectres are native to the Netherealm in that human beings can be transformed into them when their essences descend into hell, but it is unclear if Netherealm hosts any original life. It should also be noted that the inhabitants of this realm look more human than they are, because the realm's magical nature conceals their demonic nature. Once they leave the Netherealm, they may start to decompose and rot. Like Chaosrealm inhabitants, some Netherealmers tend to speak backwards.
A specific subset of demons, the Oni, is thought to be native to the Netherealm. They vary a lot in terms of appearance, stature and colour, as is evidenced by Drahmin and Moloch, and appear to be unable to communicate with other lifeforms. (Although in Armageddon's conquest mode Drahmin does state "Welcome to Hell." to Taven.) Their prime state of being appears to be one of unquenchable rage.
There are also seen dismembered humans, presumably from the Chamber of Dismembering.

Notable residents
Not born in the Netherealm 
Drahmin was once a warlord who was presumably assassinated, and transformed into a caricature of his former self by unknown powers, until he became an Oni. He may have been at the seventeenth level of Hell, seeing that he is somewhat eaten by maggotsor he might have been skinned in Hell as well.
Noob Saibot is the altered form of the elder Sub-Zero, after he was murdered by Scorpion in retribution for his own killing. The mass corruption in his soul caused him to transform into a humanoid Wraith based on his reincarnation in the next life as he is not in a very low level.
Reiko was originally introduced as a member of the Brotherhood of Shadow, presumably a demon as well. However, his exact origin is revealed as Outworld in his trading card video.
Scorpion became a vengeful specter in the Netherealm after he was killed by Noob Saibot (as Sub-Zero). Unlike most creatures in the Netherealm, Scorpion is neither evil nor good and can somewhat withstand the torturous realm better than others stating that he is not at a very low level in Hell. In fact, it has been stated that his powers increase there as of Deadly Alliance. His type of reincarnation is based on the Chinese belief that a dead person with unfinished business comes back to settle scores with opponents and can't be easily put to rest.
Shinnok was once an Elder God, descended into Netherealm because he wanted to take over Earthrealm without relinquishing his status as Elder God. However, he did overthrow Lucifer with Quan Chi's assistance and became supreme ruler of the dark realm as stated in the MK Mythologies manual but then, his side-story in Armageddon may retcon it otherwise. He is loosely based on the Chinese god of Hell Yan Wang and the Christian Satan, being deceptive and evil.
Smoke was brought to the Netherealm by Noob Saibot. It is suspected he has also become tainted with evil after his new master altered his nanotechnology.

Native or unknown
Quan Chi's origin is not known other than the fact that he used to be an Oni, but one of the Netherrealm's demons claims that Quan Chi is a demon from the Netherrealm and was a member of the Brotherhood of Shadows.
Ashrah's origins are unknown. Once an assassin in service of Quan Chi, she found a sword (Datusha) that slowly guided her to the light side.
Moloch is also an Oni, but unlike Drahmin, he is more ape-like than humanoid.
The Netherealm is also home to the Brotherhood of Shadow, led by Noob Saibot and Quan Chi.
Sareena is a demon of the realm, although little is known about her past. She was once a personal assassin of Quan Chi and served the Brotherhood of Shadow, but turned against the clan.
Kia and Jataaka were also demon assassins who served Quan Chi alongside Sareena. While they remained loyal to Quan Chi, Sareena did not.