Sub-Zero, whose real name is Kuai Liang (traditional Chinese: 快涼; pinyin: Kuàiliáng), is a member of the Lin Kuei ninja clan. His code name was originally Tundra, but following his the death of his brother, Bi-Han, Kuai Liang took his mantle.
In one version of the Mortal Kombat story, Sub-Zero's best friend Smoke was turned into a cyber-ninja, like Sektor and Cyrax. In another version, Smoke remained human, but Sub-Zero himself was turned into a cyber-ninja.
Sub-Zero is a poor bastard. He's entered the most HTTT tournaments, and never won a single one of them.