It sounds bucolic: how Timothy Treadwell, amateur naturalist, spent 13 summers in Alaska's back country, living nose-to-snout with the wildlife. Less so when you learn that he chose to camp among grizzly bears or that, in October 2003, he was killed by one of his ursine neighbors. Werner Herzog's fascinating documentary-cum-character study, Grizzly Man, attempts to discover just what motivated Treadwell to drop out of the "people's world" and live at great personal risk among the bears.
Forming the spine of the film are excerpts from more than 100 hours of video that Treadwell shot on his sojourns from 1999 until his death. Besides documenting the bears, Treadwell also kept a video diary of his hopes, fears, excitements and rages. A tow-headed, lazy-voiced dude who seems misplaced from the Southern California surf, his personal entries portray him as blindly obsessive and variously troubled -- aspects that clearly attracted Herzog, who has cast his lens over other such driven, complicated figures (Fitzcarraldo, My Best Fiend).
Herzog interlaces Treadwell's footage with expository sequences, interviews with Treadwell's colleagues and detractors, and his own ruminations on the nature of man and madness. Grizzly Man is no nature film (unless you consider man the most fascinating and ultimately unknowable creature of all), though much of Treadwell's footage depicts gorgeous country and thrilling, intimate studies of wildlife. After establishing Treadwell as the semi-well-known grizzly expert (David Letterman asks, "Aren't you afraid of getting eaten?"), Herzog works backward, unraveling Treadwell's life, revealing layers of trouble: a failed acting stint, alcoholism, a manic personality with a burgeoning taste for danger.
What Herzog discovers is that Treadwell's life among the bears was rife with paradox, centering on Treadwell's growing megalomania: He thrived on nature's wildness while openly disrespecting it; he pontificated on bears' natural ability to attack man but believed he shared a protective bond with his bear brethren. He heralded their primal beastliness, yet gave the bears silly nicknames and issued them orders in a cloying singsong.
In a remarkable bit of happenstance, Treadwell, whose footage was seemingly intended for a future documentary about his work, provided the inevitable coda of his reckless story. The attack that killed him was captured in sound by his own lens-capped camera (though it is not presented in this film). And however brave or foolish you may find Treadwell, the irony is that Herzog's film enables Treadwell, albeit posthumously, to accomplish many of his goals: to document the bears, to present his preservation concerns to a wide audience, and to be a star. Throughout the film, Treadwell frequently avers he'd willingly die for his bears or his cause, and he checked that off his to-do list as well. 
