Billboard sat down with co-directors MacMahon and McGourty to learn how they locked in interviews with Page, Robert Plant and John Paul Jones, why the film stops after Led Zeppelin II and how some of the band’s contemporaries reacted to screenings of the movie.

DECIDER spoke to director-writer Bernard MacMahon and producer-writer Allison McGourty about this project that was decades in the making.

In retrospect, it makes sense that backing Bassey would prove formative: So much of Led Zeppelin was about power, poise and drama (or melodrama, if you think of the first album's overwrought "Babe I'm Going to Leave You").

Full of never-before-seen footage of the band’s first 18 months, interviews with John Paul Jones, Jimmy Page, Robert Plant, and new audio from the late John Bonham, the first authorised documentary about the best hard rock band to ever do it assumes a lot about what its audience already knows.

No band has a greater mystique than Led Zeppelin. Now, a stunning new documentary goes inside that legend and traces their origins.