Bruce Campbell was in all three of the Sam Raimi movies, but as different bit characters in each one. Why was he used in all three movies?
There were a couple of reasons for this.
1) Sam Raimi (director) and Bruce Campbell are good friends and Bruce normally gets cameo's in his films.
2) There was a rumor before and after Spider-man 3 Bruce Campbell was going to become Mysterio as Mysterio constantly blames Spider-man for his failed acting and stunt gigs.(source)
From an interview with Bruce Campbell: