Now I'm sure that there are already MILLIONS of these theories that you have all seen. But This here is my view.
First off I would like to give credit to joewahby on steam for this article, [2016 Mythology Explained thouroughly through Codices] , which I used to help put my theory together.
Now, WHO is the DOOM Slayer. All we know is he's the silent, pissed protagonist who is shrouded in mystery. In joewahby's article, he comes to the conclusion that the DOOM Slayer is the "betrayer", the Knight Sentinal who betrayed the others in order to get his son back. In this article, joewahby says that he thinks that the DOOM Slayer is the betrayer, and that he was enraged at the Dark Lord's and desided to fight the demons because of this. He also clames that the "wretch" that gave him the suit was classic Doomguy. But I found this answer didn't satisfy me, and overlooked several things.
Let's look at what we know about the DOOM Slayer. We know he wears the "Crown of the Knight Sentinals", meaning he is there leader, obviously. We also know that he got his suit from a "wretch" and that it was forged in hell. We know that his soul was "tainted" and that he chose to stay in hell to get revenge. We also know that an angel, the Seraphim, gave him extra strengh and speed to help him. Now in joewahby's theory, the betrayer made a deal with a hell priest, tainting his soul, and he is in hell to kill the Dark Lords for making his son a demon. The wrech he calls Doomguy, and that the praetor suit used to be his. But this theory misses a few things. Now, lets talk about my theory, which I think is what is ment to be assumed.
Doomguy IS the DOOM Slayer
I know this is such a rung out theory, but hear me out, k? Lets dig into this.
The Crown of the Knight Sentinals
It says that the DOOM slayer is the leader of the Knight Sentinals. But it says nothing about the leader and the betrayer being one in the same. It actually lead me to think ohterwise. The betrayer is a father, who wanted his son back, it says nothing about the leader, other than that he's the DOOM Slayer. (big help there).
Another thing is that it never says anything about the DOOM Slayer even fighting during the conquer of Argent D'Nure. It seems like the DOOM Slayer is connected to hell through a different event. In fact, he's almost COMPLETELY isolated from the Knight Sentinals. He's a third party that the Knight Sentinals made there leader.
But WHY would they make an almost complete stranger there leader? A gap? Or something to back up my theory? I will say later.
This I have trouble with, or do I? Well, I did. The DOOM Slayer got his suit from a wretch. But who is he? Well, I looked back at DOOM 3 for this. In it, you are given your armor in the armory. Now this has no relivence, but it gave me the idea. The Doomguy is on mars because he shot his comanding officer. And his team on Mars treats him like shit until they're killed. Wreches. What if he disliked them, they would technically be where he got his armor.
There is some one in hell who gave him his suit, sorta.
The Praetor Suit
Ok WHY would this thing have serial numbers and warnings on it if it was made in Hell? Answer: IT'S NOT!
There is no way this thing was made in hell I'm gonna say that now. But this isn't the original suit, entirely. This is where I wrap up the wretch. Though there is nothing that makes this connection, I think that the wrech is the betrayer. He gave his old suit to the Doomguy, who modded his old suit with the Knight Sentinal suit. This actually explains the Praetor Suit almost perfectly. This explains why it can function like a Knight Sentinal suit (Being able to absorb Argent Energy and use it to make the wearer super-human through mutation) while still looking like a UAC suit to an extent. It also explains why the suit looks like parts of it are custom-made, because the suit was modded.
THIS makes much more sense.
His Soul is Tainted
Well whacha expect the guy's been in hell since frickin 1993!!!
This stupid joke really sums it up. The Doomguy has been in Hell for so damn long, he's been absorbing argent energy already, and somehow isn't becoming a possesed. But this gets even deeper than that.
He's been fighting demons for so long, literally locking himself up in hell, not only is he sorta mutated, his mental condition is for sure far from healthy. We see this in the simple gameplay of just about every DOOM game. This guy is brutal. The demons are his enemies and he's gonna MURDER them. Weather it be a chainsaw or a glory kill, he ENJOYS killing them in the most brutal way possible. He's a pyschopath. He's "tainted".
The Dark Lords Wronged Him
Looking at this from the angle that "The DOOM Slayer is a new character" makes this confusing, "What did they do?". But if we consider the idea that the DOOM Slayer and Doomguy are one in the same, it's clear and obvious. The demons took EVERYTHING from him.In DOOM 1 they destrouyed the Phobos and Demos bases, where Doomguy was possitioned. Then they opened a portal to Earth, killing his bunny and possably his sister (I get this from the level named "Donna to the resque' Donna is his sister). In DOOM 2 they destroyed all human cities and almost wiped out humanity. They even had the nerve to open the hell portal in Doomguy's hometown. He probably lost EVERYRTHING. His home, family, friends. It's so likely it might as well be fact. He lost it all. Adn when the Mother Demon revived the demon armies, and he went back to mars to kill them, he took a good look at it and...wanted revenge. Just as the DOOM Slayer is said to have done, Doomguy locked himself up in hell at the end of DOOM 64 to get revenge over the demons, to wipe them out of existence. There he dscovered the betrayer, the wretch (A betrayer could easily be considered a wretch), who gave Doomguy his old Knight Sentinal suit, which Doomguy combined with his UAC suit. Then, after who knows how long...
The Knight Sentinals
Why would the Knight Sentinals make Doomguy there leader? Well, lets say the Knight Sentinals didn't until after Argent D'Nure was absorbed into hell? Thsi actually fits what the Slayer's Testimant entries say. It seems they fought in hell for a while. Lets say, that there leader, however, was dead. And that they were "flying blind". Then comes along this guy. They've heard of him from the demons. A man who was able to destroy there armies, who left hell in ruins. They didn't know who he was, until they finally met him. They learned about him, and desided he's EXACTLY how they need to be there leader. So they crown this man, this, Doomguy, there leader, who leads them until the demons capture him, when they also kill the Knight Sentinals. This fits well with the facts we are given, and has much fewer gaps in it. There's only one thing
Who is he? Well, we know even less about him than we do the DOOM Slayer himself. I'm sure, however, that he helped Doomguy WELL before he got the Praetor Suit, which, I think, is why the Argent Energy didn't make Doomguy a possesed. Then he got the suit which enhanced him even MORE, making him what he is now, the DOOM Slayer.
So that's my theory on who the DOOM Slayer is. I know that tons of other people are saying that Doomguy s the DOOM Slayer, but with this I was able to back it up. Tell me in the comments who you think of my theory, or even what you think the DOOM Slayer is.