Doom's protagonist (often called Doomguy by fans, or just "Marine") is the main character of Doom and its sequels or offshoots, who is also known as the Doom marine or the Marine (the latter especially in Doom 3), as well as our hero at the end of Doom II. In all the games, this protagonist is a futuristic marine that is never specifically referred to by name.
The only thing known about the Doom marine's life prior to the events of the Doom games is that he was stationed on the Mars base in the first place because he had assaulted a superior officer who ordered him to fire upon innocent civilians. In Doom 3, on the other hand, it is specified that the player has been sent to Mars as a replacement for another marine lost in the operations. The two back stories are not necessarily contradictory.
It is implied (in Wolfenstein RPG) that the original Doomguy is a descendant of William B.J. Blazkowicz destined to confront and finally defeat the Harbinger of Doom (Cyberdemon), after Blazkowicz had successfully destroyed its left arm and right leg after it had been summoned at Castle Wolfenstein during World War II.
Understandably, many arguments have been made over the proper name for the player character, or as to whether a name would be appropriate at all. The original story and in-game cut scenes by id Software are composed in the second person, suggesting that there is no definable "Doom guy" and that the character simply stands for whoever is incidentally playing the game. John Romero has pointed out the main reason for the lack of a name for the game character by stating the following: The less you know about him, the more likely you as the player will feel free to invent your own personality for him. There was never a name for the DOOM marine because it's supposed to be YOU.
In the early Doom Bible, a character named Buddy Dacote is described in a way that, of all the characters described, makes him most similar to the game's eventual protagonist. The Doom Bible notes that Dacote stands for Dies at conclusion of this episode, and correspondingly the marine in the finished game seems to die or to be close to dying at the very end of Doom's first episode, Knee Deep in the Dead, as a result of the final ambush in the dark room after taking the anomaly's demonic teleporter.
Other products that extend the Doom franchise do provide a name for the main character. The Doom novels roughly based on the classic games give the marine the name of Flynn Taggart, and in the Doom movie, the name of the protagonist is John Grimm, nicknamed Reaper. Another game from id Software, Quake 3, includes a playable character named Doom that is presented as an incarnation of the so-called Doomguy (as well as a female version named Crash). In Doom II RPG the playable marine character is named Stan Blazkowicz, who is a descendent of William "B.J." Blazkowicz of Wolfenstein 3D. John Kane is the marine of the Doom 3 novels.
 Original Doom
The original box art portrays the protagonist as a rather muscular man wearing green armor as well as a light brown space helmet that partially conceals his facial features. The player's in-game avatar, as seen in multiplayer mode and in the ending to Doom II, is based on this depiction.
The marine's face is seen in the game's status bar, where he is shown as having light brown hair and a buzz cut. The protagonist also appears with his head uncovered in the title screen for Doom II and in the final screen for The Ultimate Doom, but in both cases displaying a more unusual haircut and wearing armor and pants of a darker hue of green.
The character's personality is never examined to any extent in any of the games, though it could be said he is passionate about battling hell's hordes as, after a new weapon is picked up, the protagonist grins devilishly, and also grits his teeth intensely when firing a weapon continually. When taking damage, the marine similarly clenches his teeth in anger and pain, and otherwise his eyes are constantly and alertly darting to and fro.
At the end of The Ultimate Doom there is a jocose tidbit about our hero, saying that the severed rabbit head shown at the end of the third episode, Inferno, is the protagonist's pet rabbit, Daisy. After completing the fourth episode, Thy Flesh Consumed, a battered marine is shown outside of a burning city on Earth, a not too seemly look of vengeful defiance on his face, with the rabbit's head clenched in his fist by the ears, and ready to wreak yet more violence on the hellish invaders.
 Doom 64
The Doom 64 marine looks almost identical to the original except that his armor is black instead of being of the same green as his clothes, his boots and helmet are black too instead of grayish beige, and his visor is blue rather than gray. Also, his helmet features a radio antenna on the side in a way somewhat reminiscent of Boba Fett's helmet in The Empire Strikes Back.
His face is never shown in Doom 64 since there is no status bar. The game's background story text implies that he is the same person from the first games, denoting him as "the only experienced survivor of the DOOM episode".
 Doom 3
In Doom 3, the Marine's appearance is roughly consistent with the above, except that his facial features are not concealed, since he does not wear a helmet. His physique is also less powerful looking, although he is still relatively muscular. He has black hair and appears to be in his mid twenties to early thirties.
Unlike in the original series, the player can "talk" to various people. Most of them do not say much (other than that they are busy and the UAC base is a frightening place), but a few, such as Sergeant Kelly, give the player some briefing regarding his mission, especially after the the forces of hell invade the UAC base. Even on these "chatting" occasions, however, the player character is addressed simply as "Marine" and remains silent, either because most of the discussion is about his orders (this is a similarity to Half-Life), or due to the silent protagonist narrative. Although the marine never truly speaks, he utters grunts of pain when injured or a scream when killed.
The Marine is depicted as tough and fearless in the game's cut scenes. He rarely shows fear or panic, despite the increasingly horrific events and creatures he comes to witness, including several bizarre and disturbing psychic visions. He only shows a brief burst of anxiety (stepping back slightly and appearing to mouth a curse) when he first sees the towering cyberdemon.
 Resurrection of Evil
In the Doom 3 expansion pack Resurrection of Evil the main character is a different Marine, also without a name. This Marine is a combat engineer, and thus is trained to operate a remote manipulation device known as the grabber. He has black shaved hair, wears blue armor, and appears to be somewhat older than the one in Doom 3, based on his heavily weathered facial features.
The game presents very little information on his background, only that he is part of a detachment of Space Marines under the command of Dr. Elizabeth McNeil, sent to investigate the UAC facility in the aftermath of the demon invasion. While investigating the Martian ruins he finds and touches the Heart of Hell artifact, which releases a wave of energy that disintegrates the rest of his squad and opens another portal to hell underneath the UAC base.
The Marine in Resurrection of Evil appears to be more anti-hero in outlook than the Doom 3 protagonist, as he seems to enjoy using the Heart of Hell, which ends up killing almost everyone else at the base. He also shows brief bursts of anger throughout the game, especially toward the Hell Hunters and Maledict.
 The Lost Mission
In The Lost Mission from Doom 3's BFG Edition, the player takes control of another unnamed Marine during the events of Doom 3, shortly after the massacre of Bravo Team in the EnPro facility. This Marine is wounded during the ambush, but manages to escape. He is eventually recruited by Dr. Richard Meyers of Exis Labs to destroy an unfinished teleporter in Hell to prevent the demons from using it to invade Earth. He succeeds and kills a Guardian-like monster before escaping back to Mars where he is eventually rescued by the Earth Fleet. The fact that he survived the events of Doom 3 may be an indication that there were other survivors and that the UAC covered up their survival.
The Lost Mission Marine's face is never shown and almost nothing about his personality is revealed.
 Doom II RPG
In Doom II RPG one of the three playable characters, named Stan Blazkowicz, bears a striking resemblance to the protagonist of the original Doom. In the game's storyline he is a descendent of William "B.J." Blazkowicz, the Wolfenstein 3D hero.
 Doom movie
John "Reaper" Grimm (played by Karl Urban) is the son of UAC scientists who were killed in an accident during the early excavation of the Martian dig site. Reaper abandoned his scientific heritage and joined the military to forget about this personal tragedy, eventually becoming a member of the elite Rapid Response Tactical Squad (RRTS). Grimm, his commanding officer nicknamed Sarge, and the other members of the RRTS are dispatched to the UAC Mars Facility to investigate the disappearance of several scientists, which ultimately pits them in a confrontation against genetically engineered monsters created by an ancient Martian retrovirus released by the UAC. Grimm also differs from the protagonists in the games due to having an actual name and interacting with other characters via his own dialogue.
Grimm's personality can be seen as rather angsty, as he is still dealing with his guilt over his parents' deaths and his concern for his sister, Dr. Samantha Grimm (also known as Sam), a researcher at the UAC Mars Facility. However, like his computer-game renditions, he has no problem killing multiple demons and even his own commanding officer, Sarge, after the latter begins to murder unarmed civilians in order to contain the outbreak.
Notably, at the end of the film, Grimm is injected with the Martian genetic material. Instead of turning into a monster, he instead gains superhuman strength, reflexes, and regenerative abilities. These powers allow him to stride through the infested base singlehandedly mowing down a small horde of demons including many zombies, several imps, a hell knight, and a demon (all seen by the audience in the game's classic first person perspective). This plot device is apparently the film's way of incorporating the berserk powerups in the games (see Berserk pack and Berserker).
 Technical information
- See Player for details on the character entity from a technical perspective.
- In Doom's opening splash screen, and in the game as a sprite, the protagonist is shown to be wearing a helmet with a visor. In the earliest known alpha version of Doom, the visor framed the screen, and was planned to be used in the way the status bar works, much like the Metroid Prime series. In Doom 3, you are seen in a few scenes not to be wearing a helmet (the first red scene in the toilets, for example). Yet, you are able to walk on the surface of Mars.
- The marine in the original Doom games is seemingly ambidextrous since he punches and fires the pistol with his left hand but fires every other weapon with his right hand.
- In vanilla Doom and accurate source ports, it is possible to get the Doomguy to make a shocked face by standing on a medikit found on a hazardous floor (such as slime or lava), due to the ouch face bug.
- In Chinese the character is known as the "Extermination Warrior" (Simplified Chinese: 毁灭战士; Pinyin: huǐ mìe zhàn shì), which is also the release name of Doom itself in China.
 Other games with references to the marine
- Duke Nukem 3D
- Quake III Arena / Quake Live
- Tony Hawk's Pro Skater 3 (featured in the PC version as a secret skater)