Val Kilmer, The Doors

Val Kilmer dove into some serious research for the role of rock legend Jim Morrison for Oliver Stone's 1991 film The Doors. Kilmer learned how to sing 50 songs by The Doors. He spent hours in the studio studying Morrison's performances, observing hours upon hours of interview footage—all in the name of capturing his essence.

Kilmer asked the cast and crew to exclusively refer to him as Jim; many members claimed that it was nearly impossible to tell the difference between Kilmer's and Morrison's singing voices. Kilmer was so invested in the role that once production came to an end, he had to go to therapy just to disconnect himself from the character. Paul Rothchild, a rock producer who knew Morrison personally, said that Kilmer "knows Jim Morrison better than Jim ever knew himself."