9. Bradley Cooper - A Star Is Born
When Bradley Cooper cast himself as Jackson Maine, the hard-drinking musician at the core of his self-directed A Star Is Born remake, it would've been incredibly easy for him to basically just play an extension of himself: Bradley Cooper, the handsome, charming music star.
And though Cooper hardly gave himself a drastic makeover to play the character, he nevertheless took subtle steps to ensure he wasn't merely playing a familiar riff on his public persona.
And so in addition to growing out his hair and beard, he had the film's makeup artist Ve Neill give him spray tans, worked with vocal coach Tim Monich to convince as a singer, and most crucially even lowered his speaking voice by an octave.
Cumulatively, these flourishes ensure that we're not simply watching Cooper singing but actively transforming himself, which in turn resulted in a well-earned Best Actor Oscar nomination.