Director James Toback's documentary about former heavyweight boxing champ Mike Tyson isn't a traditional nonfiction portrait so much as a feature-length interview, in which the retired boxer remains front and center for virtually the entire running time. The only talking head is his own, albeit one that speaks in multiple, sometimes self-contradictory voices. The movie covers a lot of ground: Even boxing fans who feel they know everything there is to know about Tyson may be surprised by the bracing candor with which he dissects his desire to fight, his penchant for overindulgence, his 1992 rape conviction, and the infamous Evander Holyfield bout that ended with part of Holyfield's ear on the canvas. Toback, a fellow traveler on the path of obsession and desire, wears down the calluses Tyson has built up over decades as a mass-media punching bag, taking the ex-fighter explicitly on his own terms, even if those terms are constantly in flux. Much too smart to pretend to give us "the Mike Tyson we never knew" or any similarly reductive postulation, Toback doesn't come to lionize or demonize, to goad his subject into a tearful breakdown (though Tyson does cry) or a climactic Frost/Nixon apologia. Instead he gives us Iron Mike in all his monolithic multitudes, and allows us, for a brief moment, to peer alongside him into the existential abyss.