

In Wolfenstein RPG, it is hinted that the Marine is a descendant of William "B.J." Blazkowicz, to whom the Marine's helmetless look in the original games bears a striking similarity. The Marine in Doom 64 is less muscular, with slightly modified green armor with black highlights, a black helmet with an antenna and a blue visor. He grins upon picking up a new weapon, and his most emotional face is seen when he has 20 hit points or more taken away during a single attack, showing a shocked face. When he takes damage, his reaction is a mixture of pain and anger. In Doom, Doom II, and Final Doom, the Marine expresses little emotion at the horror unfolding around him, maintaining a stern and alert glare, his eyes constantly darting left and right. The Marine appears without his helmet in the cover art of Doom II and in the ending to The Ultimate Doom episode IV, "Thy Flesh Consumed", where his armor and pants are a darker shade of green. The Marine's face is seen in the game's HUD, where he is shown with light brown hair, a buzz cut, and blue eyes. In multiplayer mode, the character wears green, red, brown and indigo. The player's in-game avatar, as seen in multiplayer mode and in the ending of Doom II: Hell on Earth, is based on this depiction. This image, with the addition of a shotgun clutched in his left hand, is carried over to the introduction screen of Doom. He is firing a machine gun and fighting a Baron of Hell.

On the box art for the original Doom, the Marine is portrayed as a muscular man wearing green armor and a light grey space helmet that conceals his facial features. He would go on to be the only survivor after battling on Phobos, Deimos and through Hell, ultimately teleporting to Earth where he discovers that Earth has been invaded by demons. The Marine in Doom was a soldier who, after being ordered to fire upon unarmed civilians, fatally punches his commanding officer and is transferred from Earth to Mars. In the finished product, this nearly happens to the Marine in the final level of the first episode, but he continues his adventure. "Dacote" is an acronym for "Dies at conclusion of this episode", and Buddy was supposed to be killed by a boss at the end of the planned third episode. The sole non-playable character, Buddy Dacote, bore the most similarities to the original game's eventual protagonist.

Tom Hall's original design draft, "The Doom Bible", described several planned characters, all of whom went unused in the final version. Romero said, "There was never a name for the marine because it's supposed to be ". The original game's co-designer John Romero said this was to increase player immersion. The Marine is not referred to by name in the game in the books he is referred to as "Flynn Taggart".
