[[Image:BuddiesMap01.png|thumb|One player in Doom looking at two others, Brown and Indigo, in [[MAP01: Entryway]]]]The '''player''' is, of course, [[Wikipedia:Gamer|a person playing the game]], either alone, or as one of several in [[multiplayer]] mode. Each player is also an [[Wikipedia:Avatar (icon)#Avatars in games|entity]] in the game world, having attributes such as position on the map, [[health]], and [[items]] possessed.
Since the game is in "first person", a player does not see himself or herself on the main portion of the screen, except for his or her own hand when certain [[weapons]] are selected.
In Doom, a marine's [[Status bar face|face]] is shown on the [[status bar]], where it reflects the player's health (becoming progressively bloodier as the player's health falls) and reacts to events such as being attacked, stepping on a [[damaging floor]], or finding a weapon or [[powerup]].
The player moves in response to the keyboard, mouse and/or joystick at either walking speed or running speed. The forward/backward speeds are somewhat higher than the sideways speed; these movements can be combined advantageously via [[straferunning]]. The maximum turning speed can be almost arbitrarily high when specialized [[Wikipedia:Device driver|mouse drivers]] are used (this may be considered [[Multiplayer cheat|cheating]] in multiplayer games, but is often acceptable in [[speedrun]]ning).
In a multiplayer game, the other players appear as space marines in differently colored space suits. In [[vanilla Doom]], the colors are green, indigo, brown and red. [[Source port]]s typically permit more choices of color, and sometimes more than four players. The [[sprite]]s for a player are rendered in a green suit; to draw another player, the [[Doom rendering engine|rendering engine]] remaps the shades of green to shades of the desired color.
A player spawns with 100% health, a [[pistol]], and 50 bullets. The [[fist]]s may also be used as a weapon. When respawning in vanilla Doom, everything else ([[armor]], other weapons, [[ammo]], [[powerup]]s, and [[keys]]) is lost. In [[deathmatch]] mode, an exception is made to this as players spawn with all keys. Some source ports permit respawning to other states.
In order to be playable in single player mode, a level must have a "Player 1 start" [[Thing]]. Player starts 2 through 4, typically located close by, enable [[cooperative]] play. [[Deathmatch start]] positions are usually located far from each other; one is chosen at random each time a player spawns.