Nobody was quite sure what to make of Joaquin Phoenix in the latter half of 2008. The award-winning actor, coming off a slew of critically-acclaimed performances in films like “Gladiator” and “Walk the Line,” announced that he was retiring from acting in order to focus on his hip-hop career. Over the coming months, Phoenix grew out his hair, gained weight, and was seldom seen aside from a few unfortunate public performances. On hand to capture Phoenix’s equally tragic and comic exploits on film was his brother-in-law, Casey Affleck, who has turned the tumultuous past couple of years into “I’m Still Here,” a riveting and humorous look at Joaquin Phoenix’s odd transformation.

Affleck deftly illustrates Phoenix’s feeling of being trapped as an actor in the film’s opening montage of archival media coverage, showing Phoenix using the same canned lines in interviews over and over. As Phoenix says in the first scene of original footage, “I don’t want to play the character of Joaquin anymore... Hate me or like me, just don’t misunderstand me.”

Soon after, Phoenix announces his retirement and his plans for a hip-hop career, to which the Hollywood community reacts with unanimous disbelief. From that point on, Phoenix slowly recedes into tragicomedy. Particularly baffling is the footage of the former actor standing in his homemade studio, mumbling laughably amateur lyrics to himself (“Times is crazy/Mothers be packing up their babies”). Following his first performance, Phoenix laments, “This is hard... There’s a lot of fucking judgment in this place.”

Yet despite his sad state, it is difficult to empathize with Phoenix. Footage shows him hiring prostitutes, snorting cocaine, and verbally abusing assistants. While debating which hip-hop mogul will produce his album, he causally claims, “Dre’s gonna be into it.” Phoenix slowly morphs into a slob with a beer belly and a scraggly, unkempt beard. He wears a surgical mask like a party hat for unexplained reasons, starts to refer to himself as JP, and tries to wax philosophical by posing questions such as “Do you think for a fly, wings are strictly a mode of transport?”

What makes “I’m Still Here” so darkly funny are the reactions that Affleck is able to capture in response to Phoenix’s behavior. The look on Mos Def’s face as Phoenix describes his project as a “hip-hop ‘Bohemian Rhapsody’” or Sean “Diddy” Combs’ stupefied expression as he listens to Phoenix’s demo tape and its refrain of the word “Compli-fuckin’-cation” are two truly hysterical moments.

Despite the frequent comedy, Affleck also provides an unflinching look at the dark side of Phoenix’s lifestyle. Backstage following his infamous, disastrous appearance on Letterman, Phoenix is left speechless. During the limo ride afterwards, he climbs out and breaks down, worrying that he’ll be considered a “fucking joke” forever. Phoenix’s torment at this stage in his reinvention is palpable.

Affleck’s portrait of a talented artist tortured by himself, the public, his peers, and the media climaxes with Phoenix performing in a Miami nightclub. As he begins to mumble his way through a halfway-decent beat, the club grinds to a halt. No longer is anyone dancing, but it appears as if everyone in the building has pulled out a cell phone or camera to capture the trainwreck. One of Affleck’s recurring visual motifs—that of Phoenix displayed on a large number tiny screens simultaneously—serves as an overt but stirring comment about our contemporary celebrity culture, one based largely on voyeurism and schadenfreude.

There has been a lot of public speculation about whether or not Phoenix’s retirement was a hoax. Quite frankly, it doesn’t matter. Regardless of whether Joaquin Phoenix is truly chasing his hip-hop dreams or if the whole thing is a work of conceptual art, “I’m Still Here” captures a celebrity during a major transition and attempted reinvention. It’s a blackly humorous, at times pitiable look at how Phoenix has turned himself into a walking punch line. Though it may seem paradoxical, career suicide could end up making Phoenix more famous than he had ever been before.

—Staff writer Brian A. Feldman can be reached at bfeldman@college.harvard.edu.