Seriously, this fucking guy
Prior to 2005, Reese Witherspoon was best known for playing the ditzy lawyer in Legally Blonde or for playing the ditzy ______ in _______. Then came Walk the Line. By simply adopting a southern accent, dying her hair black and not cringing as Joaquin Phoenix spent two hours making Johnny Cash look like the victim of severe head trauma, Witherspoon walked away with her first Academy Award for Best Supporting Actress.
Other Famous Examples Include:
Robert Downey, Jr. in Chaplin
Bill Paxton in Apollo 13
Cate Blanchett in Elizabeth
Hell, Phoenix got nominated for Best Actor also. Seriously, this shit cannot fail. Unless you make one crucial mistake (foreshadowing alert!).
The Exception That Proves the Rule:
As insane as he may be, you have to admit Russell Crowe is also a pretty shitty musician. Fortunately for him, he's an actor. Up to a few years ago, Crowe got nominated every time he managed to leave the house without hurling a phone at somebody. Hell, it almost seemed like cheating when he took the starring role in the biopic Cinderella Man, in which he played a blue collar boxer who gave America something to root for during the Great Depression.
Crowe's depiction of former heavyweight boxing champ James J. Braddock was almost universally praised. After SAG and Golden Globe nominations, he put on his Oscar crapping diapers and got ready for an Academy Award nomination ... that never came.
Crowe forgot that to get your biopic performance lauded as ingenious, you have to pretend to be someone the Academy has heard associated with the word genius, or at the very least someone they've heard of in the first place. Braddock was a blue collar boxer and a family man. Hell, the guy didn't even have a heroin problem. Crowe might as well have been playing Gandhi.
Astute readers will point out that Ben Kingsley took home an Oscar for playing Gandhi, and that Robert De Niro took home an Oscar for playing a decidedly non-brilliant boxer. But astute readers are about to get served by trick number five ...