Doom

Doom (typeset as DOOM in official documents) is a 1993 science fiction horror-themed first-person shooter (FPS) video game by id Software. It is considered one of the most significant and influential titles in the video game industry, for having ushered in the popularity of the first-person shooter genre. The original game is divided into three nine-level episodes and distributed via shareware and mail order. The Ultimate Doom, an updated release of the original game featuring a fourth episode, was released in 1995 and sold at retail.

In Doom, players assume the role of an unnamed space marine, who became popularly known as 'Doomguy', fighting his way through hordes of invading demons from Hell. With one third of the game, nine levels, distributed as shareware, Doom was played by an estimated 10 million people within two years of its release, popularizing the mode of gameplay and spawning a gaming subculture. In addition to popularizing the FPS genre, it pioneered immersive 3D graphics, networked multiplayer gaming, and support for customized additions and modifications via packaged files in a data archive known as 'WADs'. As a sign of its effect on the industry, first-person shooter games from the genre's boom in the 1990s, helped in no small part by the game's release, became known simply as 'Doom clones'. Its graphic violence, as well as satanic imagery, made Doom the subject of controversy.

Doom, a science fiction/horror themed video game, has a background which is given in the game's instruction manual; the rest of the story is advanced with short messages displayed between each section of the game (called episodes), the action as the player character progresses through the levels, and some visual cues.

The player takes the role of an unnamed space marine ('Doomguy') who has been punitively posted to Mars after assaulting his commanding officer, who ordered his unit to fire on civilians. The Martian space marine base acts as security for the Union Aerospace Corporation, a multi-planetary conglomerate, which is performing secret experiments with teleportation by creating gateways between the two moons of Mars, Phobos and Deimos. Mars is considered by space marines to be the dullest assignment imaginable. This all changes when the UAC experiments go horribly wrong. Computer systems on Phobos malfunction, Deimos disappears entirely, and 'something fragging evil' starts pouring out of the gateway, killing or possessing all UAC personnel.

Responding to a frantic distress call from the overrun scientists, the Martian marine unit is quickly sent by ship from Mars to Phobos to investigate, where the player character is left to guard the perimeter with only a pistol while the rest of the group proceeds inside. The marine hears assorted radio messages, gunfire, and screams, followed by silence: 'Seems your buddies are dead.' The player cannot navigate the ship off of Phobos alone and sees that the only way out is to fight through the Phobos complex.

As the last man standing, the player character's mission is to fight through the entire onslaught of demonic enemies by himself in order to keep them from attacking Earth. Knee-Deep in the Dead, the first episode and the only one in the shareware version, is set in the high-tech military bases, power plants, computer centers and geological anomalies on Phobos. It ends with the player character entering the teleporter leading to Deimos, only to be overwhelmed by monsters.

In the second episode, The Shores of Hell, the marine has successfully teleported to Deimos. He fights his way through installations on Deimos, similar to those on Phobos, but warped and distorted from the demon invasion and interwoven with beastly architecture. After defeating the titanic Cyberdemon, the marine discovers the truth about the vanished moon: it is floating above Hell.

The third episode, called Inferno, begins after the marine climbs off Deimos to the surface. The marine fights his way through Hell and defeats the Spider Mastermind that planned the invasion. Then a hidden doorway back to Earth opens for the hero, who has 'proven too tough for Hell to contain'. However, a burning city and a rabbit's head impaled on a stake (named in The Ultimate Doom as the marine's pet rabbit, Daisy) show that the demons have invaded Earth, setting the stage for Hell on Earth. The sequel retcons the events of Doom as an alien invasion of the Mars moon bases.

In The Ultimate Doom expansion, in the fourth episode Thy Flesh Consumed, it tells that the marine fought valiantly against the hordes of demons that the Spider Mastermind sent through that hidden doorway but ultimately the forces of Hell prevailed in the invasion of Earth. The locales of Thy Flesh Consumed are varied, including a mix of high-tech bases and demonic temples, though the atmosphere appears to be Earth.