The game revolves around three species: the Terrans, human exiles from Earth; the Zerg, a super-species of assimilated life forms; and the Protoss, a technologically advanced species with vast mental powers. Wings of Liberty focuses on the Terrans, while the expansions Heart of the Swarm and Legacy of the Void will focus on the Zerg and Protoss, respectively. The game is set four years after the events of 1998's StarCraft: Brood War, and follows the exploits of Jim Raynor as he leads an insurgent group against the autocratic Terran Dominion. The game includes both new and returning characters and locations from the original game.
Wings of Liberty features approximately the same number of units as the original StarCraft. Some units from the original game have returned, some featuring new upgrades and abilities. For example, the Protoss Zealot, a melee unit from the original game, now has the researchable ability to dash forward and quickly reach nearby enemies as a refinement of its speed upgrade from the original. Other units have been replaced or removed entirely. Other changes to unit design have been inspired by story events in StarCraft and its expansion, StarCraft: Brood War, replacing old units with new or renamed versions which sport different attributes and abilities. Units in StarCraft II have new abilities, compared to the original, that encourage more complex interaction with the game environment.