When Marty McFly returns from 1955 in the first Back to the Future film, a man sleeping on a park bench witnesses his return. Is this man someone I should've recognised, from before the timeline was altered by the events in 1955?
Who was this bum?
No, you should not have recognized him as this was his first appearance in the film. Although, he does appear in the sequel.
There was a fan theory that Red was former Hill Valley Mayor, Red Thomas. However, according to Bob Gale's commentary on the Back to the Future DVD set, the name of the bum was ad-libbed by Michael J. Fox.