First introduced in Mortal Kombat: Deception, the One Being is considered to be the progenitor of the Realms of Mortal Kombat (Earthrealm, Netherrealm, Outworld, Orderrealm, Chaosrealm, Edenia, and others yet to be mentioned in the storyline). According to 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 second 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 devour the Elder Gods and destroy all of reality.
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 Elder God 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 and Shao Kahn into absorbing all realms, as a means of making itself whole again.
- According to reversed languages of Chaosrealmers/Netherrealmers, all the existence is only dreams of the One Being since his consciousness was shattered into what become the Realms.