Sub-Zero is one of the most popular characters in the Mortal Kombat series. There are in fact two incarnations of Sub-Zero, and they are siblings: the older brother Bi-Han, and younger brother Kuai Liang. Both are blue garbed warriors that are members of the Lin Kuei that descended from Cryomancers: an Out world race possessing the ability to generate and control the powers of ice, although both of them were born in Earthrealm. Kuai Liang bears a scar on his right eye which he received between the events of MKII-MK3. However - as of Deception - the scar has faded away, possibly because of the effects of his Dragon Medallion.
In their biography, both Sub-Zero brothers were sons of a Chinese Cryomancer father and a human mother. It is known that the father of both brothers was a secret operative for the Lin Kuei in the United States. He married an American woman and together they had two sons. Against the will of their mother, the father took the sons with him to move back to China, and as such both brothers were trained as Lin Kuei assassins. This was later ret conned as both brothers being kidnapped by the Lin Kuei (this was revealed in Sub-Zero's trailer in Mortal Kombat 2011).
Bi-Han appeared as Sub-Zero in the first Mortal Kombat, while Kuai Liang went by the codename "Tundra". After Bi-Han was killed by Scorpion during the tournament, Kuai Liang replaced him for the rest of the games - Bi-Han later became the undead Netherrealm wraith, Noob Saibot.