Who is Sub-Zero?
Sub-Zero is the enigmatic blue ninja of the Lin Kuei. The Sub-Zero in the Mortal Kombat series is actual two seperate characters. The "original" Sub-Zero appeared in Shaolin Monks, Mythologies and the original Mortal Kombat. His younger brother, the current Sub-Zero has appeared in all other games except for Special Forces. Sub-Zero has also appeared in both Mortal Kombat movies, the TV Series, and the cartoon.

The elder Sub-Zero was sent on a quest to recover Shinnok's amulet at the request of the Lin Kuei grandmaster and the sorceror, Quan Chi. Along the way he met a rival ninja, Scorpion, and brutally killed him. After the mission, Rayden revealed to Sub-Zero that he had been tricked, and sent him to the Netherealm to recover the amulet. Sub-Zero did and Rayden then invited him to join the Mortal Kombat tournament, where he was slain by Scorpion, who was now a specter.

The younger Sub-Zero refused to become automated like three of his fellow Lin Kuei, Smoke, Cyrax and Sektor and went on the run. After a few years, he took control of the Lin Kuei in a battle with Sektor and began reforming it for the forces of good. He acquired the Dragon Medallion, which greatly enhanced his powers, but also made him appear decades older than he was. He took on an apprentice, Frost, who betrayed him and froze herself solid. He buried her in an ancient cavern in Outworld, where he found and put on the armor of what he perceived to be his ancestors.

The younger Sub-Zero ran into his older brother, who was now a wraith going by the name of Noob Saibot. Noob had also aquired his brother's former friend, Smoke, who was now doing the wraith's bidding.