u/LivingPomelo2943

I was watching a video about all the choices you could make in the I Know You RDR1 side mission and I tought maybe the Strange Man are multiple souls or people in body, the Strange Man says things to John like he knows him from all over the place

(''I Know you from Mexico, and I know you from back out West I know you from all over!'').

This could mean that every singe person that John murders manifests into the Strange Man. This could explain why the Strange Man said that he cant remember his name, there is a lot of names, he cant die because he is already dead, he says he's an accountant, he accounts every soul John kills. He says that John doesn't remember Heidi McCourt's face and that he is forgetting about a lot of people, those people are the people murdered by John. He also said

''We have to stop meeting like this John''

( 10:40 of this video https://www.youtube.com/watch?v=K4Ky_9Ljpxo )

Dutch also says that in his last encounter with John before dying so this could make sense, Dutch's soul joined the Strange Man. He also talks to John strangely, he sometimes calls John

friend or old friend

many times which seems normal but if we follow this theory we could see that someone there who knows him very well is telling him this, he said

''You kill people so easily, yet you respect the vows of marriage. That's very curious''

which also looks normal until you see

''You kill people so easily''

representing all the souls trapped in Strange Man talking to John. The Strange Man is like a grim reaper but he keeps the souls. What if these souls are vengative souls

(John : I'll let the appropiate authorities judge my morality, friend

Strange Man : Yes, you will and they shall. )

they shall, these are the souls that will judge John's morality, Strange Man also say that John is famous from killing a lot of banditos, these banditos are Strange Man, Everyone whose death was provocated by John is the Strange Man. If you analyse the video

( https://www.youtube.com/watch?v=K4Ky_9Ljpxo )

you will notice a lot of these similarities. Those are vengative souls that took vengeance on John Marston after he shot the Strange Man 3 times condemning the life of Uncle, Abigail and Himself, John. He shot the Strange Man just where his grave would be. Maybe if John listened to Arthur's advice

(Revenge is a fool's game)

he could have reedemed himself, but instead he went to hunt Micah. Not knowing that he was hunting himself too.

About RDR2, as many people know there is a cabin in this game which is full of weird stuff and a painting, this painting will slowly evolve into a Strange Man portrait, that you can only see as John (I believe) and when this portrait is finished if you go into first person and look yourself into the mirror, the Strange Man will be there right behind you, you cant touch him, you cant shoot him, he is only a reflection, a reflection in John's back, a permanent reflection of every kill John will make from that point forward (since he killed Micah and got a revenge), this could represent that the Strange Man will start collecting these souls and watching every single step that John makes. And if you screenshot this cabin and look at the screenshot in Rockstar Social Club, the screenshot will be named

''Serial killer''

This is probably how all the souls inside the Strange Man look at John, as a reckless serial killer. The RDR1 side missions is called

''I Know You''

Because the Strange Man has been watching John for all those years, the Strange Man knows everything about him, because of the souls.

This is all I have to say for my theory, thanks for reading.