"Doom is a series of first-person shooter video games developed by id Software. The series focuses on the exploits of an unnamed space marine operating under the UAC (Union Aerospace Corp.), who fights hordes of undead and demons in order to survive. The series was widely considered as one of the pioneering first-person shooter series in the video game industry, introducing features such as 3D graphics, true third dimension spatiality, networked multiplayer gameplay, and support for player-created expansions with the Doom WAD format. Since Doom, which was released in 1993, the series has spawned three sequels, numerous expansions and a film."
Source: Wikipedia, "Doom_(series)", available under the CC-BY-SA License.