Documentaries engineered by a subject's estate deserve a dose of skepticism. Access to rare materials is no small thing, but complete artistic control tends to make for better art. In the style of family-approved documentaries like Tupac: Resurrection and Montage of Heck, British director Stevan Riley drew from more than 200 hours of private audio recordings to construct Listen to Me Marlon's voice-from-beyond-the-grave narration.
Marlon Brando talks about the mother from whom he inherited his sense of the absurd, the father from whom he inherited his contempt for authority, and the acting coach with whom he honed his craft. He went on to become a two-time Oscar winner, a civil-rights advocate, and a chronic womanizer (about which he explains, "Past a certain point, the penis has its own agenda"). Riley provides a privileged view of Brando's thought process, and he doesn't overlook the personal tragedies (his daughter's suicide) or the mid-career misfires (1968's Candy), but the lack of outside voices ensures that the film is always on his side.
To get a fuller picture, it's worth seeking out two documentaries that lack the Brando family seal of approval: Hearts of Darkness, which details the making of Apocalypse Now, and Lost Soul, which does the same with the mind-bogglingly misbegotten Island of Doctor Moreau.