Sgt. Stan Blazkowicz (aka Sarge) is a protagonist (out of a choice of three) in Doom 2 RPG.
He is based on the generic Space Marine characters from the Doom series.
He is a member of the Union Aerospace Corporation's Space Marines. They traveled to Tycho station on the moon in preparation to investigate the Mars Incident when a demonic imcursiom began in the station.
Stan would help save the universe from the demons alongside Riley O'Conner, and Kira Morgan.
One of them would ultimately fight a Cyberdemon in hell.
Behind the scenes
Stan Blazkowicz's reuses the artwork of the previously unnamed Marine of the Doom I/II using the same artwork (and he may be intended to be the same character from those games, or at least a fellow marine, although not necessarily the same 'timeline'). The novels of Doom give the marine in those games the name Flint Taggart but deviate from the storyline of the main Doom series with extraterrestrial aliens having created the demons rather than actual demonic entities. Doom 3 novels gives the marine of that series the name John Kane. Fans unofficially referred to all of them collectively as "Doomguy".
The character (or separate character) is nameless in Doom RPG (simply referred to as the Marine as in Doom I/II), alluded to in Wolfenstein 3D, and given a name in Doom 2 RPG. He is however not the default character in Doom 2 RPG, which defaults on Kira Morgan instead. He is one of three choose able characters in the game. While the Marine character is intended to be the same (or based on the same character), the introduction dialogue suggests that the events of the previous game were "mysterious occurrences involving classified incident of a UAC containment problems on Mars", and that the three individuals are sent to the Moon to begin 'investigations' suggesting that Stan, Kira and O'Connor had no previous experience of the events on Mars, however the comic does imply that at least one of them knows of the events at Mars (Kira Morgan, the platoon leader) although she doesn't know exactly what happened, and it is more clear that they are investigating further outbreak on the Moon, and other colonies. However, the comic suggests that Stan Blazkowicz is not the same Marine from Doom RPG, as he appears to have never encountered zombies, and even Kira figures out that they must be "zombies".
There were no known survivors of the Doom RPG/Doom 3 Mars attack (the marine in Doom 3 was actually found after the Doom 3 incident but the fate of him and those whom rescued him are not known). However comparisons to timeline might suggest its possible that Doom RPG may take place a year after the Doom 3, and closer to Doom RPG2, and that the incidents in doom 3 and RPG are two separate incidents.
The comic also adds one of the hints that Doom 3/Doom RPG maybe more or less concurrent to each other in the same universe but separate Marines (if they are in the same universe, but Doom II RPG is a sequel) (the marine in Doom 3 is said to be John Kane in its related novels). Interestingly Phobos is referenced in Doom RPG, foreshadowing possible future invasion point there (a reference to Doom I), and there are rumors foreshadowing possible invasion of Earth (forshadowing Doom II).
The Marines facial animations in the early Doom games are very similar to those of B.J. Blazkowicz in the Wolfenstein 3D games, and they have roughly similar builds.
B.J.'s sprite or at least his face makes a cameo appearance in Doom II RPG as the mysterious "Caldex', the commander of Tycho Moon station.