DOOM

Doom has a science fiction/horror theme and simple plot. A background story is given in the game's manual, and the rest of the story is advanced with short messages displayed between each section of the game (called episode), the action as the player characterprogresses through the levels, and some visual cues.
The player takes the role of a nameless space marine, "one of Earth's toughest, hardened in combat and trained for action", who has been punitively posted to Mars after assaulting his commanding officer, who ordered his unit to fire upon civilians. The Martian marine base acts as security for the Union Aerospace Corporation(UAC), a multi-planetary conglomerate, which is performing secret experiments with teleportation by creating gateways between the two moons of Mars, Phobos and Deimos. The manual makes it clear that Phobos is considered by space marines to be the dullest assignment imaginable: "with no action for fifty million miles, your day consisted of suckin' dust and watchin' restricted flicks in the rec room." This all changes when the UAC experiments go horribly awry. 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 to Phobos to investigate, where the player character is left to guard the hangar with only a pistol while the rest of the group proceeds inside. Over the course of the next few hours, the marine hears assorted garbled radio messages, gunfire, and screams...then silence: "Seems your buddies are dead".
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. [4] In order for the game to be completed, the marine must fight through Phobos, Deimos, and then Hell, each presented as an episode containing nine distinct levels. 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 fighting a pair of Barons of Hell and afterward entering the teleporter leading to Deimos, ending with him getting overwhelmed by monsters, if not killed. In the second episode, the Shores of Hell, the character journeys through the installations on Deimos, areas of which are interwoven with beastly architecture, warped and distorted by the hellish invasion. After defeating the titanic Cyberdemon lord, he discovers the truth about the vanished moon: it is floating above Hell itself. After climbing down to the surface, the third episode, called Inferno, begins. After the huge Spiderdemon that masterminded the invasion is destroyed in the final mission,


on the higher of the game's five difficulty levels often encountering a dozen or more in the same room. There are 10 types of monsters (Doom IIdoubles this figure), including possessed humans as well as specifically hellish monsters of varying strength, including the weak but ubiquitous imps, the floating cacodemons, and the bosses which survive multiple strikes even from the player character's strongest weapons. The monsters have very simple behavior, consisting of either walking toward their opponent, or attacking by throwing fireballs, biting, and scratching. They may also sometimes fight each other after hurting one another accidentally.