An enigmatic and otherworldly character, the Strange Man appears to know John Marston very well, including details about his past life in the Van der Linde gang that not even John himself remembers. The Strange Man dresses in a black three-piece suit with a black tie and black top hat.
Red Dead Redemption 2
There is an abandoned shack in Bayall Edge, Lemoyne that seems to belong to the Strange Man. The shack is riddled with cryptic writing alluding to Armadillo, Herbert Moon and the cholera outbreak of New Austin. If the player visits it as Arthur Morgan, there will be an unfinished painting of the Strange Man. If the player visits the shack as John Marston, the painting will gradually become more and more complete over the next few days, and John will document his thoughts of it in his journal, saying how it makes him feel "fascinating, awful and seductive, all at once". John can also see the Strange Man stalking him in the mirror like a phantom.
A stranger in New Austin, around Hennigan's Stead, alludes to the Strange Man. He states how a man wearing a "black suit and big top hat," whom he believes to be the Grim Reaper, haunts and curses the town of Armadillo, being the reason for the Cholera epidemic.
Herbert Moon has a portrait of the Strange Man in his general store, similar to the one in Bayall Edge, though much smaller. John will notice and asks about it, claiming he recognizes the man, but Herbert Moon shrugs it off, saying that somebody gave it to him and that he has it in his store because he likes it.
Red Dead Redemption
The Strange Man is the focus of the stranger side-mission "I Know You", which is only available for John Marston. John meets the Strange Man in three separate places during the mission, once in each territory of the game. Each time, the man gives vague answers to John's questions, and twice, asks John to perform errands for strangers. The first is to visit a man about to cheat on his wife, the second is to visit a nun trying to raise money for charity. The player can either do the right things by stopping the man and donating to the nun respectively, or do the wrong things by encouraging the man to cheat on his wife and robbing the nun. The Strange Man appears one final time overlooking Beecher's Hope. He is unforthcoming about who he is, and his standoffish demeanour enrages John enough to open fire on him. The Strange Man is completely unaffected and mysteriously vanishes right before John's eyes.
In an issue of Gamepro Magazine, a closer look at Red Dead Redemption was given. When asked about the Strange Man quest, and whether the "man in the black top hat" represented God or Satan, Rockstar told the magazine that they could not tell if the Strange Man was God, Satan, or anything else.
Red Dead Redemption
During the third encounter with the Strange Man, he says, "This is a fine spot". This location later serves as John, Uncle and Abigail's gravesites.
Near the end of the encounter John fires three bullets at him, but before he could fire a fourth, his gun jams. It is possible the three bullets symbolizes John, Uncle and Abigail dying in "The Last Enemy That Shall Be Destroyed", and the fourth one jamming represents Jack being spared.
It is possible to kill the Strange Man; the player has to shoot him before triggering the cutscene, but doing so will fail the mission.
The player cannot kill him once the mission is complete.
The Strange Man can be "killed" right after the second encounter. He will appear to have died and the body can be looted. Doing so does not affect the "I Know You" side missions in any way.
If the player points a gun at him, he can pull out a Cattleman Revolver and shoot and kill the player. He may also run away while yelling at John.
After the first encounter with him, players can point a gun at him and he will start to run. If he is hogtied, he will keep talking as if the situation were normal. However, pointing a gun at him is considered a crime and civilians will attempt to alert law enforcement.
The Strange Man is the only character John meets within all three territories of the map.
If the player attacks the Strange Man he will say things like, "You always were a nasty little orphan", "Come now, Marston", or "You haven't changed".
There's a portrait of the Strange Man in John's bedroom at Beecher's Hope
Red Dead Redemption 2
If the player takes a screenshot of the Strange Man's cabin and uploads it to the Rockstar Social Club, it will list the photo's location as "Serial Killer".
In the epilogue, John can visit the General Store in Armadillo, where he will notice a picture of the Strange Man owned by the shopkeeper. John will say that he looks familiar, despite not seeing him until the events of Red Dead Redemption which occur four years later.
There is a dead alligator beneath the Strange Man's cabin.
It's heavily alluded to that Herbert Moon is associated with the Strange Man. In the cabin, there is a map of Armadillio with a hand written note which reads "I offered you happiness or two generations. You made your choice". This could be in reference to the Cholera outbreak and possibly allude that it was caused by a deal with the Strange Man. This is further backed up by a letter that can be looted from Herbert Moon himself. The letter details the marriage of Herbert's daughter and that she is pregnant. This is likely what the "two generations" line from the note is referencing. In the cabin one can find writing on the wall saying "The Moon Will Shine On In The Darkness". Incidentally Herbert Moon is one of the only residents of Armadillo not infected or harmed by the Cholera outbreak.
By using trainers to swap Arthur/John's models, the player may notice that the Strange Man's model is named "mysteriousstranger". It's possible that the Strange Man was heavily inspired by Satan from Mark Twain's "The Mysterious Stranger", as both seem to be enigmatic, supernatural entities, while also frequently questioning humanity's hypocrisy and moral paradoxes.
Paintings in the Strange Man's shack change depending on Arthur or John's honor level. High honor will display paintings of eagles and bucks. With low honor the paintings will show vultures and coyotes. A poem about the fate of Jimmy Brooks also changes depending on if Arthur spared him or murdered him.
Yes, many have...
—The Strange Man's last words
Why would you remember me, friend? You've forgotten far more important people than me.
—The Strange Man
You kill people so easily, yet you respect the vows of marriage. That's very curious, John.
—The Strange Man
This is a fine spot.
—The Strange Man referring to what will later become John's gravesite
We have to stop meeting like this John.
—The Strange Man before meeting John for the last time
Marston, what a coincidence!
—The Strange Man before the last encounter.
If it isn't my old friend.
—The Strange Man "surprised" to see Marston again.
The Strange Man with John
A picture of the Strange man in Red Dead Redemption 2
Painting of the Strange Man in Red Dead Redemption 2
It’s behind me isn’t it.
Red Dead Redemption "I know You" Strange Man Theories
Red Dead Redemption 2 - Meeting Herbert Moon who has a picture of the "I Know You" Stranger
Red Dead Redemption 2 - John finds a painting of the Strange Man
Red Dead Redemption 2 Easter Egg - The Strange Man