NEW YORK (Bloomberg) ¿ Watching the Clash take the stage at London's 100 Club in 1976, film director Julien Temple was convinced that Joe Strummer's new band was doomed to fail. Temple was sceptical of Strummer's sudden switch from long- haired hippie squatter to short-haired, peroxide-blond punk. The first few chords of "London's Burning" changed his mind.

"It took about two seconds to realise he could totally pull it off," Temple said in a telephone interview from his home in Somerset, England.

Strummer's journey to self-proclaimed "punk rock warlord" is one of many transformations noted in "Joe Strummer: The Future is Unwritten''. In the two-hour documentary, which opened at the weekend in New York and Los Angeles, Temple gives equal time to Strummer's virtues and weaknesses.

Temple, 53, was familiar with both. He met Strummer, born John Mellor, in 1976 and filmed the band during its early days. Two decades later, the friendship was rekindled after both bought homes in Somerset. They were neighbors when Strummer died suddenly from an undiagnosed heart defect in 2002.

"Joe was very flawed and ruthless and cowardly at times," Temple said. "I couldn't have been his friend if his generosity and inspirational qualities hadn't hugely outweighed that." "The Future is Unwritten" renews Temple's examination of Britain's punk movement of the late 1970s and early 1980s. He directed two films about the Sex Pistols, "The Great Rock 'n' Roll Swindle" (1980) and "The Filth and the Fury" (2000). Formed a few weeks before their appearance at the 100 Club, the Clash surpassed the Sex Pistols as punk's leading band. Hits including "White Riot'', "London Calling" and "Rock the Casbah" made them international stars whose concerts filled stadiums around the world. Ultimately, success destroyed the Clash. Drummer Topper Headon was fired because of heroin addiction. Then Strummer, worried that the band had strayed from its political focus, kicked out his chief collaborator, guitarist Mick Jones, in 1983. Strummer re-formed the band with new personnel but the music failed to catch on. The group disbanded two years later.

The film follows Strummer as he changes his name to Woody (an homage to folk singer Woody Guthrie), drops out of art school and works odd jobs, including a brief stint as a gravedigger.

Switching identities again, Strummer grew his hair long and took up the name by which he became famous. He joined the squatter movement, hippies who illegally occupied abandoned houses in West London, and formed a band, the 101ers, that gained a following in London pubs.

Strummer's identity changed again in 1976 after the 101ers performed as the opening act for the Sex Pistols. Impressed by the band's energy and aura, he turned his back on the 101ers and within a month had cut his hair short, dyed it blond and joined the Clash as lead singer. Strummer kept his stage name, but adopted a cockney accent to hide his middle-class background.