In the late 1960s and throughout the 1970s, four gifted British musicians took center stage as the biggest rock band in the world – Led Zeppelin. Born in 1968 out of their predecessors, the Yardbirds, the quartet of lead singer Robert Plant, guitarist Jimmy Page, bassist John Paul Jones and drummer John Bonham took the US and UK by storm with their unique fusion of hard rock tinged with blues, folk and supernatural influences. The band subsequently became the first group to unseat the Beatles from the top of the music charts – quite a feat, even if the Beatles were on the verge of breaking up at the time – and released a string of blockbuster LPs that eschewed the typical “singles” approach previously employed by other artists, a shift perfectly timed to cater to the emerging “album rock” format of many underground and independent FM radio stations. Their origin story is now brought to life in writer-director Bernard MacMahon’s documentary feature, chronicling how Led Zeppelin came together and running through the time of their ascendancy as the premier rock band of a new decade. The key to appreciating this film, however, is understanding a key word in its title – “becoming.” The filmmaker specifically focuses on the careers of the four musicians before they came together as Led Zeppelin and what happened during the newly formed band’s infancy, amassing a following that exploded over the course of roughly two years. In recent interviews with Plant, Page and Jones, as well as excerpts from a previously unreleased archive conversation with Bonham (who died in 1980), viewers learn about their diverse upbringings, their various musical influences, the impact of a volatile and radically changing culture at the time and their respective performance careers prior to the group’s formation, largely as studio session musicians. Through these dialogues, audiences can see how these elements came to characterize them both individually as artists and collectively as Led Zeppelin. This material reveals a number of interesting tidbits about the band and its members, such as Jimmy Page’s work as a session guitarist on the theme song to the James Bond film “Goldfinger” (1964), as well as the little-known source of the renamed group’s new moniker, a suggestion made by drummer Keith Moon of The Who. Diehard fans are sure to appreciate the meticulous level of detail presented here, though casual followers and the unfamiliar might just as easily see it as overkill. That’s especially true given that the film’s narrative feels like it stops short of its potential. Wrapping up the picture early on in the band’s career may leave some viewers disappointed, especially since the film pays no attention to the group’s later (and perhaps better-known) work, such as details about their classic cuts on subsequent albums. Consequently, some might see this film as being “incomplete,” almost as if it were the first installment of a longer production, such as the kind of documentary miniseries that one might view on PBS or one of the cable network music channels. Nevertheless, there are also qualities that make this a stand-out work, such as showcasing the arguably underrated virtuosity of the band’s four members, musicians whose talents likely haven’t been regarded as highly as they maybe should have been over the years. It also makes clear how the band was more than the sum of its parts, how each of these performers came together to create something greater than just the fusion of four individual talents. And, for those who grew up during the period of the band’s birth (as I did), this offering truly is a finely constructed piece of nostalgia, one that definitely tugs at highly personal memories of a remarkable time that hasn’t been repeated since. So, when considered in total, “Becoming Led Zeppelin” is probably best viewed as a mixed bag that some will likely worship as much as they do the band itself, while others may find it a modestly engaging, albeit “unfinished” introduction to one of the most monumental rock bands of all time. And, in that sense, then, the picture might be best typified by a paraphrase of one of Led Zeppelin’s iconic song titles – what is and what will never be.