The Doom Slayer is the protagonist and playable character of Doom, Doom II: Hell on Earth, Final Doom, Doom 64, Doom (2016) and Doom Eternal. He has also guest starred in the Quake games such as Quake Champions and Quake III Arena. The demons of Hell first gave him the appellation "Doom Slayer" and also refer to him as the Unchained Predator, the Beast, and the Hellwalker. The UAC refers to the Doom Slayer as DOOM Marine, or The Slayer.
Before the character had any epithets in the story, he was most commonly called Doomguy in the fan community. This nickname is mentioned in Doom Eternal and used in his dialogue subtitles.
He is intended to be the latest iteration and continuation of the classic DOOM Marine who is the protagonist for most of the series. According to Tom Hall and John Romero (who worked on the original Doom), the original iteration of the DOOM Marine was the grandson of Commander Keen and the great-great-grandson of William J. Blazkowicz.