With a trio of films in the mid-1950s - A Streetcar Named Desire, On The Waterfront and The Wild One - Marlon Brando laid claim to being the greatest actor of his time. He was also a cultural icon before that phrase was cheap: a magazine cover fleetingly seen in this film asks, "Could There Have Been Elvis Without Brando?".
Yet his career as a whole was a chain of disappointments, studded with professional failures and personal tragedy.
Even our memories of its great later high point, the revelatory title-role performance in The Godfather, are sadly overshadowed by his legendary obesity and the fates of two of his 15 (or so) children: son Christian shot and killed his sister Cheyenne's boyfriend in 1990; Cheyenne committed suicide in 1995.
Writer-director Riley, who made Fire in Babylon, the exuberant ode to the era when the West Indies owned world cricket, studiously eschews superficial gossip in this deeply impressive documentary, which adopts an impressionistic, poetic style that is entrancing and deeply revealing.
There's more than enough to keep the casual Brando fan happy, but the film gets under the skin of its subject largely by letting him do almost all the talking.
The provenance of the title doesn't become clear until the closing minutes, though it tantalises us throughout: is it an instruction to himself? To us? To him by another?
The fact that it can be all three is among the film's many charms. Drawing on the huge personal archive (mainly audio, but video, too) that the actor compiled with an eye to posterity, Riley creates what might be called a mash-up, though that word risks understating the meticulousness of his approach.
Sweeping back and forth through time, interleaving public record with private rumination, and matching images and words often recorded decades apart, Riley brings to vibrant life a tormented genius, the son of a bully father and a drunkard mother who never overcame his sense of being unwanted and unloved.
In doing so, he gives us Brando by Brando, warts and all: irresistible flirt; passionate activist; a man crippled and beset by guilt and anxiety. It's a mesmerising look at one of the greats who was, finally and for all that, just a man.
Cast: Marlon Brando
Director: Stevan Riley
Running time: 103 mins
Rating: M (offensive language)
Verdict: A doco befitting its subject