Doom (stylized as DOOM) is an American media franchise created by John Carmack, John Romero, Adrian Carmack, Kevin Cloud, and Tom Hall. The series usually focuses on the exploits of an unnamed space marine (often referred to as Doomguy or Doom Slayer) operating under the auspices of the Union Aerospace Corporation (UAC), who fights hordes of demons and the undead in order to save Earth from an apocalyptic invasion.

The original Doom is considered one of the first pioneering first-person shooter games, introducing to IBM-compatible computers features such as 3D graphics, third-dimension spatiality, networked multiplayer gameplay, and support for player-created modifications with the Doom WAD format. Over 10 million copies of games in the Doom series have been sold; the series has spawned numerous sequels, novels, comic books, board games, and film adaptations.

Overview
The Doom video games consist of first-person shooters in which the player controls an unnamed space marine commonly referred to as Doomguy; in the 2016 series, the protagonist is called the “Doom Slayer” or just “Slayer” in later entries. The player battles the forces of Hell, consisting of demons and the undead. The games are usually set within sprawling bases on Mars or its moons, while some parts take place in Hell itself. The classic series had only a limited focus on the story, much of which was present in the manuals rather than the games themselves. More recent titles, particularly the 2016 series, would feature a heavier focus on narrative.

The original game featured eight weapons, designed in such a way that no weapon became obsolete after the acquisition of another. With the player carrying all of these weapons at once, the strategy of “gun juggling”—rapidly switching between the weapons depending on circumstance—can be employed. Outside of combat mechanics, Doom levels often feature mazes, colored key cards and hidden areas. Due to technical limitations, the player could not jump or look up and down in the classic series. These features were added in newer titles.