The Fire God is a character that debuted in Mortal Kombat Mythologies: Sub-Zero and acted as one of the bosses.
He was one of four guardian gods assigned by Raiden to guard the Amulet of Shinnok in the Temple of Elements and acted as the god of fire in the Mortal Kombat universe. He had the ability to teleport, fire jets of flame, as well as to perform a burning chokehold. He was the final elemental god defeated by the elder Sub-Zero, allowing the ninja access to the amulet.
In the official Mortal Kombat 4 comic that came with the PC version of said game, the younger Sub-Zero attempts to make peace with the temple guardians, but discovers that they are gone. This could indicate that the Fire God was killed by Shinnok during his invasion, an idea further substantiated by Fujin's Mortal Kombat 4 biography screen stating that he and Raiden are among the few surviving Earthrealm gods.
The Fire God appears in the film Mortal Kombat: Annihilation, discussing with the Water Goddess about Earth's fate. During the climax of the film, he and the Water Goddess arrived to stop Shinnok's treachery and declared Mortal Kombat. After Liu Kang and his friends defeat Shao Kahn and his minions, the Elder Gods imprison Shinnok and have his son Raiden take his place.
In Liu Kang's non-canonical Mortal Kombat (2011) ending, he asks the Elder Gods to give him a chance to defeat Raiden and take his current position as protector of Earthrealm after defeating Shao Kahn. He succeeds in defeating the former God of Thunder, becomes the new protector of Earthrealm and seems to become a God of Fire (reflecting the element Liu Kang used in battle as a mortal). In Shang Tsung's non-canonical Mortal Kombat (2011) ending, Liu Kang becomes a god and Shang Tsung must learn how to control his new-found power to defeat his old foe.