While aging fallout 4 for a bit I noticed the mysterious stranger seemed to be a little suspicious even though the game tries to give you the "just go with it" attitude I did a little digging... After watching a video on top 10 facts about fallout by: lemmino learned about vault 11.

Vault 11 was an experiment to that took 1000 people and told them that if they don't sacrifice 1 person then all of them will die. They began with a democratic system by voting on who died.later on people demanded a lottery to randomly pick who died... after pandemonium broke out and there were only five survivors. They agreed to not sacrifice anyone else and when the time of death came they would kill themselves...

A year passed by and nobody was killed. They finally found out that that's what the experiment was truly about, it wanted to see how long it would take for the people to revolt... after seeing that everyone sacrificed was for no reason four of the survivors killed themselves leaving one survivor that survivor then left the vault and was never heard from again. That one survivor is the Mysterious Stranger. Any thought on this?

That there is no answer to who he is and there is never meant to be one, because its in the name, Mysterious Stranger, he is meant to never be explained, simple as that.