4. Val Kilmer Needed Psychiatric Assistance To Separate From Jim Morrison - The Doors
Few actors have ever committed to a single role harder than Val Kilmer did to play Jim Morrison in The Doors, spending six months learning 50 of the group's songs, only 15 of which actually appeared in the film.
Despite the generally mixed reception to the film, Kilmer's performance was widely praised amid speculation he might even receive a Best Actor Oscar nomination - which ultimately, sadly, he didn't.
Years later, Kilmer admitted that he had trouble disentangling himself from not merely playing such an iconic figure but basically becoming him both before and during shooting.
Kilmer wore some of Morrison's real clothes, asked to be referred to as "Jim" on set, and spent as long as five gruelling days filming single musical scenes during the shoot.
Ultimately Kilmer had to seek psychiatric assistance to remove Morrison's aura from his own mind, and so it's not terribly surprising that the actor has never since committed to a role quite so aggressively.