Depending on your age, the protagonist of the Doom series is either Doomguy, a name lovingly given by the community, or Doom Slayer, a title provided by the demons of Hell in Doom 2016 and Doom Eternal. One of his co-creators has weighed in to settle the debate, and he believes the former is ultimate canon.
John Romero, co-creator of Doom, and co-founder of id software, responded to a tweet looking for the appropriate nomenclature for the Doom marine. His response? "Doom Guy's name is Doom Guy." Simple and straightforward, cut and dry, no more questions needed. As if Romero's authority on the subject needed any more underlining, in replies he points out that he was there when the guy was born, which is a bit of a mic drop on any further comment.
The notion of giving Doom Guy some sort of formal designation is a modern concept in the FPS games. Doom 2016 and Doom Eternal have the classic marine referred to as Doom Slayer in the lore, using the mythology to reflect the actual reputation of Doom as a whole. On his old forums, Romero himself wrote that the hero was anonymous in first-person because "it's supposed to be YOU", playing down the canonical relevance of the Doom spinoff novels at the time.
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