Joaquin Phoenix established himself as a serious actor with roles as Commodus in "Gladiator" and Johnny Cash in "Walk the Line," but then he did some experimenting. When Phoenix announced his retirement from acting in 2008 and made a shocking appearance on David Letterman saying he was becoming a rapper, no one knew what to think. Finally Phoenix came clean in 2010, announcing that his stunt was a performance piece for Casey Affleck’s mockumentary “I’m Still Here.” Although unseen since then, Phoenix has recently proven himself with his critically acclaimed comeback in Paul Thomas Andersen’s “The Master,” a role many are saying is his best yet. (Photo by Getty Images)