One small line from Native American poet and activist John Trudell’s 17,000-page FBI file flashes on screen in Heather Rae’s biographical film: “He’s extremely eloquent . . . therefore extremely dangerous.” That eloquence led Trudell to the forefront of the American Indian Movement (AIM) in the ’60s with the occupation of Alcatraz island, and it’s kept him on the cutting edge of musical performance poetry since the 1980s. In February 1979, hours after he burned a US flag in a Washington protest, his wife, children, and mother-in-law were burned alive in a fire of suspicious origin. By Trudell’s on-screen account, that terrible event moved him to become a poet and performer, roles to which this philosopher and naturalist patriot — with his movie-star looks and earthy voice — is especially suited. Through the testimonials of friends and family as well as interviews with Trudell and archival footage of his performances and history-making exploits at Alcatraz and at South Dakota’s Pine Ridge Reservation, where the feds managed to dismantle AIM, Rae gets not only into Trudell’s head but under his skin. The movie is a fascinating blueprint of how a daring free-thinker is wired.