14. MICHELLE WILLIAMS

Movie: My Week with Marilyn (2011)
While watching My Week with Marilyn, the audience might forget that it's a film from 2011 that stars Williams as the 1960s Hollywood icon. She completely loses herself in her troubled character. For the role, Williams gained weight, wore padding around her hips, studied Monroe’s films and interviews to pick up her mannerisms, and apparently kept her persona between takes.