Warren Evan Spector is an American role-playing and video game designer, director, writer, producer and production designer. He is known for creating immersive sim games, which give players a wide variety of choices in how to progress. Consequences of those choices are then shown in the simulated game world in subsequent levels or missions. He is best known for the critically acclaimed video game Deus Ex that embodies the choice and consequence philosophy while combining elements of the first-person shooter, role-playing, and adventure game genres. In addition to Deus Ex, Spector is known for his work while employed by Looking Glass Studios, where he was involved in the creation of several acclaimed titles including Ultima Underworld, Ultima Underworld II, System Shock, and Thief: The Dark Project. He is employed by OtherSide Entertainment, where he was part of the development team for now-cancelled System Shock 3. He is currently working on a new immersive sim based on an original intellectual property.

An immersive sim (simulation) is a video game genre that emphasizes player choice. Its core, defining trait is the use of simulated systems that respond to a variety of player actions which, combined with a comparatively broad array of player abilities, allow the game to support varied and creative solutions to problems, as well as emergent gameplay beyond what has been explicitly designed by the developer. This definition is not to be confused with game systems which allow player choice in a confined sense or systems which allow players to easily escape consequences of their choices.