Ermac is a fusion of souls destroyed in Outworld's wars. He was put under the control of Shao Kahn and his shadow priests. Appearing loyal to the forces of evil at first, the blind swordsman Kenshi freed him on Kahn's control. Ermac decided to join the forces of good and help Liu Kang free the his friends from Onaga's grasp. Like most characters, he was killed in the war of Armageddon.
In the new storyline, Ermac is devoted to Shao Kahn, fighting for him at command. He sucessfully ripped off Jax's arms in battle, making the need for cybernetic ones.