DOOM was the first in a series of first-person shooters created by id Software. DOOM was first released in 1993 for DOS as shareware. The game is considered to have to firmly established the first-person shooter genre, following in the footsteps of Wolfenstein 3D. The success of DOOM prompted id Software to create a sequel, DOOM II: Hell on Earth. The game was later repackaged as The Ultimate DOOM, including the original name plus a new episode, Thy Flesh Consumed.
The company United Aerospace Corporation (a.k.a. UAC) is the sole source of funding and supplies and oversees to all Mars base dealings. In addition to UAC occupying the bases on Deimos and Phobos, Marines are kept there, making it more of a military base. However, some believe that while UAC has been making technology to help us, they have also been dealing in illegal portal research. You, a new marine, pick up something on your radar coming from the Phobos base, an anomaly of sorts. However, when you arrive there, you find that the whole crew has been turned into zombies. Armed with your lonely pistol, you fight through the base to see just 'what the hell is going on'.
The objective of each level is simply to locate the exit room that leads to the next area (usually labeled with an inviting red EXIT sign), while surviving all hazards on the way. Among the obstacles are monsters, pits of radioactive slime, ceilings that come down and crush the player, and locked doors for which a key card, Skeleton key, or remote switch need to be located. The levels are sometimes labyrinthine (the auto-map is a crucial aid in navigating them), and feature plenty of hidden secret areas that hold power-ups as a reward for players who explore.
DOOM is notable for the weapons arsenal available to the player, which became prototypical for first-person shooters. The player starts armed only with a pistol, and brass-knuckled fists in case the ammunition runs out, but larger weapons can be picked up: these are a chainsaw, a shotgun, chain gun, a rocket launcher, a plasma rifle, and finally the immensely powerful BFG 9000. There are a wide array of power-ups, such as a backpack that increases the player's ammunition-carrying capacity, armor, first aid kits to restore health, the berserk pack (a black first aid box that puts the character into berserk mode, allowing them to deal out rocket launcher-level damage with their fists and potentially splattering former humans and imps), and supernatural blue orbs (called Soul Spheres) that boost the player's health percentage beyond 100%, up to a maximum of 200%.
The enemy monsters in DOOM make up the central gameplay element. The player faces them in large numbers, on the higher of the game's five difficulty levels often encountering a dozen or more in the same room. There are ten types of monsters (DOOM II: Hell on Earth doubles this figure), including possessed humans as well as demons of different strength, ranging from weak but ubiquitous imps and red, floating cacodemons, to the bosses which survive multiple strikes even from the player's strongest weapons. The monsters have very simple behavior, consisting of either walking toward the player or attacking by throwing fireballs, biting, and scratching (though they can also monster fight each other).
Many versions of DOOM (and its sequels) include secret levels which are accessed by the player discovering alternate exits, often hidden behind secret doors or in difficult-to-reach areas. In some versions of Doom II: Hell on Earth, two of these secret levels incorporate level design and characters from DOOM's precursor, Wolfenstein 3D.
Aside from the single-player game mode, DOOM features two-player multi-player modes playable over a network: "co-operative", in which two to four players team up against the legions of Hell, and "deathmatch", in which two to four players fight each other.
- Chain gun
- Rocket launcher
- Plasma rifle
- BFG 9000