As Sub Zero's name, clothes, and powers would suggest, his character was icy and distant. In all aspects, he was a cold-blooded and violent assassin absolutely dedicated to his clan, the Lin Kuei. While essentially neutral, his soul had become dark and corrupted from years of violence and remorseless killing. Before his story is revealed to the player, the player can make an educated guess on who he was. He disappears after MK, and reappears in MKII reborn as Noob Saibot.
When he died in the first Mortal Kombat tournament at the hands of Scorpion, his soul; corrupted by years of violence, descended to the Netherrealm's Fifth Plane. The evil within his soul was released, stripping him of pride, compassion, and everything else, "humanly normal." He wishes to not only to remain in the Netherrealm, but to conquer and rule it. Though he has been seen in the service of conquerors such as Shinnok and Shao Kahn, his ultimate allegiance is to himself.