Doom is the first installment in the Doom series, and one of the games that cemented the first-person shooter genre. With a sci-fi/horror style, it gives players the role of marines who find themselves at the center of an invasion from Hell. The game introduced deathmatch and cooperative play in an explicit sense, and helped foster the practice of allowing and encouraging fan-made modifications of commercial video games. It was first released on December 10, 1993, when a shareware copy was uploaded to a University of Wisconsin FTP server. In 1995 The Ultimate Doom was released, an updated version of the original game that included a fourth episode.

In Doom, players assume the role of an unnamed space marine, popularly nicknamed "Doomguy" by the community before becoming Doom Slayer, who fights hordes of invading demons from Hell. With one-third of the game, nine levels, distributed as shareware, an estimated 15 to 20 million people played Doom in the two years following its release, popularizing the gameplay and spawning a video game subculture. In addition to popularizing the FPS genre, it pioneered immersive 3D graphics, networked multiplayer gameplay and support for custom additions and modifications through files packaged in a data file known as "WADs". As a sign of its effect on the industry, the first-person shooter games of the genre boom of the 1990s, aided in no small part by the game's release, came to be known simply as "Doom clones." Its graphic violence, as well as satanic imagery, made Doom the subject of considerable controversy.

The Doom franchise later continued with the sequel Doom II: Hell on Earth (1994) and numerous expansion packs, such as Master Levels for Doom II (1995) and Final Doom (1996). Originally released for PC DOS, the game was ported to different operating systems for PC, MAC and consoles, such as the Super Nintendo / Super Famicom. When the game's source code was released in 1997, even more adaptations emerged, as fans ported the code to countless devices. The series began to lose popularity when Doom's engine technology became outdated in the mid-1990s, although fans have continued to create wads, speedruns and modifications of the original. The franchise returned to popularity in 2004 with the release of Doom 3, a horror-focused game using id Tech 4, with an associated Doom movie in 2005. Another installment, simply titled Doom and powered by id Tech 6, was released in 2016 and focused on returning to the fast-paced action of the first two games. In 2019, a second Doom movie, titled Doom: Annihilation, was released. On March 20, 2020, Doom Eternal, a sequel to Doom (2016), was released.

Development of Doom began in late 1992, with John Carmack writing the new game engine while the rest of id Software was finishing Spear of Destiny (the prequel to Wolfenstein 3D). When the full design phase began in late 1992, the main thematic influences were the movies Aliens and Evil Dead II, and the Dungeons and Dragons campaign the developers had been playing, in which the forces of Hell invaded the material world. The title of the game was chosen by John Carmack:

"There's a scene in The Color of Money where Tom Cruse [sic] shows up in a pool hall with a custom pool cue in a case. "What do you carry in there?" someone asks. "Doom," Cruse replies with a cocky grin. That, and the resulting carnage, is how I saw the game's presentation to the industry.
Id's programmers had to resort to several tricks to make these features run smoothly on 1993-era PCs. Most significantly, Doom's levels are not actually three-dimensional: they are rendered internally on a two-dimensional plane, with height differences added separately (many games still use a similar trick to create huge outdoor environments). Doom also has a low-detail mode to improve frame rates on slower PCs, such as those with an 80386 processor.

Designer Tom Hall wrote an elaborate specification document called the Doom Bible, according to which the game would feature a detailed storyline, multiple player characters, and a number of interactive features. However, many of his ideas were discarded during development in favor of a simpler design championed primarily by John Carmack, resulting in Hall being forced to resign from id Software. Most of the final level designs are by John Romero and Sandy Petersen. The graphics, by Adrian Carmack, Kevin Cloud and Gregor Punchatz, were created in a variety of ways: while much of it was drawn or painted, several of the monsters were digitized from clay or latex sculptures, and some of the weapons are modeled after toy guns from Toys "?" Us. The heavy metal/ambient soundtrack was provided by Bobby Prince.

Doom's main distinguishing feature at the time of its release was its "3-D" graphics, which were then unmatched by other real-time rendered games running on consumer hardware. Several new features enhanced those of Wolfenstein 3D:

Altitude differences (all floors and ceilings in Wolfenstein 3D have the same height), but not sloping surfaces.

Non-orthogonal walls (all walls in Wolfenstein 3D follow a rectangular grid). However, all walls in Doom are still perpendicular to the floor and/or ceiling.
Complete texture mapping of all surfaces.

Variable light levels (all areas of Wolfenstein 3D have the same lighting). This not only made the structure of each map visually more authentic, but also contributed to its atmosphere and gameplay by using darkness to scare or confuse the player.

A less static architecture than in Wolfenstein 3D: platforms can move up or down, floors can be raised sequentially to form staircases.