First introduced in Mortal Kombat: Deception, the One Being is considered to be the progenitor of the Realms of Mortal Kombat (The six major realms of Earthrealm, Netherrealm, Outworld, Orderrealm, Chaosrealm, Edenia, and all of the other smaller realms). According to an ancient legend, in the beginning of time, there only existed the One Being and the Elder Gods. The One Being fed on the essences of the Elder Gods, but eventually, the Elder Gods defeated the One Being, and, in efforts to weaken the One Being's near-infinite power, the Elder Gods separated the One Being's consciousness into the realms and created six Kamidogu, which held the essence of the One Being. The legend decrees that if one were to obtain all six Kamidogu with the Sacred Amulet, he or she would be granted ultimate power.
The One Being's disembodied consciousness seeks to reunite all the realms in order to make itself whole again. It is implied that it has acted through beings such as Onaga and Shao Kahn, and is responsible for their attempts to merge all realms - particularly Earthrealm - into Outworld.
Although the storyline of Deception would seem to hint that the One Being would be the villain of the next title, Mortal Kombat: Armageddon, this was later proven false, as Blaze would end up as the final boss in this game. The One Being is only mentioned twice in Armageddon: once in a passing statement about the kombatants "tapping into the power that make the realms", which may or may not refer to the One Being, and more directly by name during Kai's game ending.
In Mortal Kombat (2011), Shao Kahn is hinted at being under the influence of the One Being as he stands atop the pyramid, prepared to begin Armageddon and destroy the realms. This event, in the second timeline, is hastened to the final events of Mortal Kombat 3, when Shao Kahn has almost merged Earthrealm with Outworld, and at the same time he is ending all things in existence. However, the Elder Gods intervene and destroy Shao Kahn, thereby halting whatever plans the One Being may have had.
In the Mortal Kombat X comic series, it is revealed that the six Kamidogu, now daggers in the rebooted timeline, have all tasted the blood of the One Being and its essence lives within them, serving as the source of the daggers' Blood Magik.
In Shinnok's Mortal Kombat X ending, the fallen Elder God succeeds in re-merging all the realms to reawaken the One Being, allowing it to destroy all of reality upon the One Being's revival and devoured the Elder Gods.
Mortal Kombat 11 references the One Being twice:
- A dialogue interaction in with Jade and Cetrion, Jade mentions that some Outworlders pray/hold faith in the One Being.
- (non-canon) The Krypt inside Goro's Lair. The One Being's Door requires the following items of the One Being: Mind, Soul, and Heart.
From the fact that it fed off of the essences of the Elder Gods it could be concluded that the One Being holds the powers of each one of the Elder Gods, giving it nigh-omnipotence. It could also be concluded that it has control over time/space, reality, and all lives within the realms. It has also influenced powerful individuals, such as Onaga, Shao Kahn and quite possibly Shinnok; into absorbing all realms (and their denizens, given the latter's tower ending), as a means of making itself whole again.
- The One Being only makes a physical appearance in one scene in the entire franchise, during Shinnok's (non-canon) Arcade Ladder ending in Mortal Kombat X.
- According to reversed languages of Chaosrealmers/Netherrealmers, all of existence is only dreams of the One Being since his consciousness was shattered into what became the Realms. It is also stated that the Elder Gods' tendency to not directly interfere in the affairs of the realms is often due to fear of waking the One Being.
- However, in Mortal Kombat (2011 video game), Raiden comes to them hoping they would intervene when Shao Kahn invades Earth. They decline, however, as, even though Shao Kahn did break the rules, they care more about the jeopardy of the realms as a whole than one realm. However, when Shao Kahn finally does step into the Earthrealm and states his intention of conquering all, the gods intervened seeing Shao Kahn as a threat and saving Raiden who was about to face the same fate as his future self. The gods possessed Raiden's body and used him to defeat Shao Kahn and destroy him for his insolence and presumably to prevent the potential return of the One Being.
- Jade references the One Being as the God before Gods.
- Despite the fact that Titans are parent like figures to the Elder Gods like Kronika was to Shinnok and Cetrion and probably other Titans to other Elder Gods, The One Being can be considered a primordial being who may be based on Chaos from Greek Mythology "the first living being from which everything was born" according to Cetrion's mirror intro when she says "We all are children of the One Being, As are all gods of the realms".