Doom

Doom is a first-person shooter developed by id Software and originally released for MS-DOS in December 1993. Its fast action, atmospheric audiovisual design and freely distributed shareware episode helped establish the first-person shooter as one of the defining genres of the 1990s.

The player controls an unnamed space marine stationed on Mars after attacking a superior officer who ordered him to fire on civilians. When teleportation experiments conducted by the Union Aerospace Corporation open gateways to Hell, the marine's unit is sent to Phobos and quickly wiped out. Left alone, he must fight through the overrun bases of Phobos, the vanished moon of Deimos and finally Hell itself.

The original registered DOS release contains three episodes of nine levels each, including one secret map per episode. Progress combines rapid combat with exploration: players search interconnected rooms and corridors, activate switches, operate lifts, collect coloured keycards and uncover hidden areas. Varied floor heights, changing light levels and non-orthogonal walls give the environments a convincing sense of depth, although enemies and many objects are represented by two-dimensional sprites.

The arsenal grows from a pistol and the marine's fists to shotguns, a chaingun, rocket launcher, plasma rifle, chainsaw and the destructive BFG 9000. Ammunition, health and armour must be managed while confronting former human soldiers and increasingly dangerous demons, each with recognisable attacks and weaknesses. Five difficulty settings alter enemy placement and aggression, while network play allows cooperative exploration or competitive deathmatch for up to four players.

Doom was also designed to be modified: its levels, graphics and sounds are stored separately from the main program in WAD files, encouraging players to create and exchange their own material. Together with the shareware distribution model and multiplayer support, this openness gave the game an unusually long life and influenced both commercial development and fan communities. The 1995 retail edition The Ultimate Doom added a fourth episode, while the original DOS release remains the version on which the many later console conversions were based.