Joaquin Phoenix is the younger brother of deceased young actor River Phoenix. While older brother River was a widely praised up and coming actor who ultimately died (via drug overdose) before he could reach his full potential as an actor, Joaquin ultimately avoided his older brother's fate and DID become the sort of brilliant and successful film career that his brother would have surely had if not for his death.
In 2008, Phoenix announced that he's retiring from acting and wants to become a professional musician, mainly in the genre of rap. No one seemed to know if he was serious or pulling an Andy Kaufman. A documentary, I'm Still Here, made by his brother-in-law, Casey Affleck was released in 2010. It featured Phoenix acting crazy, and it didn't help to answer the question. On September 16th, 2010, Affleck revealed that the whole thing, going all the way back to Phoenix's switch to a musical career, was a big hoax, and in effect, the most extensive character that Phoenix has put together yet.