It appears as though there is some confusion amongst the populace in regard to the lore of Doom 2016 and Doom Eternal. Allow me to clear this up for you...
1. DoomSlayer and Doomguy are two(2) entirely different people. Doom 2016 is a reboot of Doom 1, not a continuation from Doom 64. Doom Eternal will be a reboot of Doom 2: Hell on Earth. Doom 64 has nothing to do with Argent D’nur between the time he Doomguy goes to Hell and the time when he is captured. Therefore, they cannot be the same person as the timeline is completely broken.
2. DoomSlayer is not human. He is a humanoid with distinct human features, but he is a native of Argent D'Nur. He was once their king and the leader of the Night Sentinels.
3. After losing his son in combat, the anguished DoomSlayer made a pact with a demon priest to resurrect him and in turn transformed his son's soul into the Icon of Sin and causing Argent D'Nur to be subjugated by Hell. DoomSlayer is The Betrayer.
4. Some lesser minded individuals have come to the conclusion that DoomSlayer is actually Doomguy, who was left in Hell in Doom 64 and eventually discovered by the Night Sentinels during the First Age. This is obviously incorrect, as the inhabitants of the dimension he returns to (our dimension) are completely oblivious in regards to the existence of Hell (with the exception of certain high-ranking UAC personnel) . Such an idea is preposterous as the entire earth was destroyed and humanity was nearly wiped to extinction in Doom 2.
Note: Headcanons regarding "alternative dimensions" which resemble the original dimension in every conceivable way sans the demonic invasion are retarded and belong solely within the minds of the aforementioned lesser-minded folk.
TL;DR: Fuck jannies and fuck you.