Sub-Zero is the name of a fictional character in the Mortal Kombat fighting game franchise by Midway Games/NetherRealm Studios. The identity of Sub-Zero is primarily assumed by playable character Kuai Liang in the series, who debuted in Mortal Kombat II (1993) and has appeared under the alias in all but two of the franchise's games. Prior to Kuai Liang, the alias is utilized by his older brother Bi-Han in the original 1992 game, who appears in subsequent installments as Noob Saibot.

Both incarnations of Sub-Zero are depicted as warriors from the fictional Lin Kuei clan who possess the innate ability to control ice in many forms. The two also share a bitter rivalry with the undead specter Scorpion due to Bi-Han killing him prior to his resurrection and Kuai Lang attempting to avenge Bi-Han's death at his hands. In contrast with his older brother's more anti-heroic and later villainous role in the series, the second Sub-Zero typically adapts a heroic persona as one of the fighters helping defend Earthrealm against various threats.

One of the Mortal Kombat franchise's signature characters, Sub-Zero has appeared on a variety of official series merchandise and alternate media, and has received both positive critical and public reception.