First, he grew a huge beard.  Then, he imploded on David Letterman back on 2/11/09, announcing in a bizarre mumbly voice that he was quitting acting to become a rapper:

Now he's the subject of a documentary by Casey Affleck entitled I'm Still Here.

Except, it's not a documentary.  It's fiction.  As was the Letterman appearance and Pheonix's behavior. From the NYT:

CASEY AFFLECK wants to come clean.

His new movie, “I’m Still Here,” was performance. Almost every bit of it. Including Joaquin Phoenix’s disturbing appearance on David Letterman’s late-night show in 2009, Mr. Affleck said in a candid interview at a cafe here on Thursday morning.

“It’s a terrific performance, it’s the performance of his career,” Mr. Affleck said. He was speaking of Mr. Phoenix’s two-year portrayal of himself — on screen and off — as a bearded, drug-addled aspiring rap star, who, as Mr. Affleck tells it, put his professional life on the line to star in a bit of “gonzo filmmaking” modeled on the reality-bending journalism of Hunter S. Thompson.

“I’m Still Here” was released last week by Magnolia Pictures to scathing reviews by a number of critics, including Roger Ebert, who wrote that the film was “a sad and painful documentary that serves little useful purpose other than to pound another nail into the coffin.”

“The reviews were so angry,” said Mr. Affleck, who attributed much of the hostility to his own long silence about a film that left more than a few viewers wondering what was real — The drugs? The hookers? The childhood home-movie sequences in the beginning? — and what was not.

Virtually none of it was real. Not even the opening shots, supposedly of Mr. Phoenix and his siblings swimming in a water hole in Panama. That, Mr. Affleck said, was actually shot in Hawaii with actors, then run back and forth on top of an old videocassette recording of “Paris, Texas” to degrade the images.

“I never intended to trick anybody,” said Mr. Affleck, an intense 35-year-old who spoke over a meat-free, cheese-free vegetable sandwich on Thursday. “The idea of a quote, hoax, unquote, never entered my mind.”

Still, he acknowledged that Mr. Letterman was not in on the joke when Mr. Phoenix, on Feb. 11, 2009, seemed to implode his own career by showing up in character as a mumbling, aimless star gone wrong.

Unfortunately, the rest of the article focuses on what Casey Affleck is doing next, and not so much Joaquin.