Who/What is The Strange Man?
From RDR Wikia:A mysterious and metaphysical character, there are several interpretations of the character's strange behavior and apparent supernatural abilities. None have been confirmed, although much of the evidence points to him being a Saint Peter figure, shown by his description of himself as 'an accountant... in a way', which could refer to the common Christian belief that Saint Peter waits at the gates of Heaven to welcome the deceased and makes record of them. He later reminds John that he will be responsible for his actions, referring to Divine Judgement. Moreover, he tells Marston that he has forgotten 'far more important people' than himself, likely referring Marston's lack of belief in God. During his appearance in Mexico, the fact that his mode of transport is a mule rather than a horse suggests humility and possibly intentional poverty/selflessness, hinting further at a Saintly figure. Also, the last encounter with him takes place at the site of Marston's grave, which the Strange Man notes is 'a fine spot'. Despite this, there are many interpretations of the true nature of the Strange Man.
It is possible that the developers did not base the Strange Man on any religious figure, whether it be Saint Peter, (a) God or Death. This is supported by the fact that no matter if the player chooses the honorable or dishonorable way of completing the task, he will always say "I hope my boy turns out to be just like you."It is also possible that he is a manifestation of John Marston's sense of right and wrong, testing his morals and forcing John to make decisions on matters he may have seen or heard about previously. The Strange Man reveals a detailed knowledge of John Marston's history. He is impeccably dressed in a three piece suit with a large top hat. The man appears to be calm and collected, even in the arid wilderness. He is also able to identify John Marston whenever Marston approaches him, without actually looking at him. When questioned, he claims to be "an accountant... in a way" but also claims he cannot remember his own name.
What year does the game take place in?
The map in the game says it's 1910, but it has been stated the game takes place in 1911.
Is Undead Nightmare a separate story? Or part of RDR?
Undead Nightmare is an expansion story, which actually takes place after John returns to his family in between the levels The Outlaw's Return and The Last Enemy That Shall Be Destroyed. While in the game, it could simply be days that pass for the player, but in terms of the story a few months go by. As we see many characters that survived through the story of RDR return in Undead Nightmare, most of whom are killed off. Also, characters that died in the RDR story will return as zombies in the graveyards. That being said, there are two continuity errors in Undead Nightmare. First, MacDougal mentions Nastas and neither MacDougal or John seem to recall him being dead, and also Uncle was killed during the mission "The Last Enemy That Shall Be Destroyed" yet he is also zombified and killed at the beginning onf Undead Nightmare.Undead Nightmare ends with John saving his family, and stopping the plague. Then we flash forward to a few months passed RDR where John has been dead and buried to see Seth unwittingly unleash the undead plague once again. At which point John rises from the grave as the body of a zombie with the soul of a man in order to continue to fight the undead hoard.