History is written by the victors—and as a corollary, winners usually become the focus of music documentaries. When it comes to the tragic tale of the Band, guitarist and main songwriter Robbie Robertson definitely has emerged triumphant. Three of the five members of this influential rock group are dead, and the other survivor, keyboardist Garth Hudson, shuns the spotlight. With Once Were Brothers, Daniel Roher presents a conventional contextualizing rock doc with marquee-name talking heads—Van Morrison, George Harrison, Bruce Springsteen, et al.—and efficiently reveals Robertson's early family life (his mother was indigenous, his father Jewish) and musical evolution. Robertson is an articulate, passionate memoirist; the film is based on his 2016 autobiography, Testimony. With equanimity, he registers the Band's soaring highs and devastating lows, while his French ex-wife Dominique adds crucial observations about the inter-band dynamics and substance abuse that dogged the members. Tracing a story of relentless, upward mobility through the music industry, the doc emphasizes Robertson's inner strength and boundless ambition, which helped him to avoid the booze- and drug-related pitfalls that afflicted his mates.