Trailer! Joaquin Phoenix in 'I'm Still Here'

Remember when actor Joaquin Phoenix went a little haywire, quit acting, grew facial hair, mumbled on "David Letterman" and announced he was going to be a rapper?

Here's the trailer for "I'm Still Here," the documentary showing Phoenix's transition -- and transformation -- directed by his good friend, actor Casey Affleck.

Was it real or just an act? Let us know what you think in the comments below! "I'm Still Here" begins a limited run in theaters starting September 10th.