"Sub-Zero is the name given to two fictional video game characters from the Mortal Kombat series. Being brothers, both of them were born in the Earthrealm, and are blue-garbed assassins that descended from Cryomancers, an Outworld race possessing the ability to generate and control the powers of ice, which gives Sub-Zero the innate ability to control ice in many forms.
A mainstay to the series, Sub-Zero is the only character in the series to be playable in every game, with the exception of Mortal Kombat: Special Forces. The older Sub-Zero first appeared in the first Mortal Kombat game, getting replaced by his younger brother in Mortal Kombat II and the subsequent games. In Ultimate Mortal Kombat 3 and most versions of Mortal Kombat Trilogy, both the elder and younger Sub-Zero appear as playable characters. Sub-Zero also appears in many other Mortal Kombat media works such as the Mortal Kombat live action film series and animated series."
Source: Wikipedia, "Sub-Zero_(Mortal_Kombat)", available under the CC-BY-SA License.