Elon Musk is the subject of Alex Gibney’s nearly four-hour documentary Musk, which premiered in Venice.

Genius, madman, salesman: Elon Musk is the subject of a nearly four-hour documentary at Venice that seeks to unmask the billionaire provocateur with outsized global influence in business, politics and even outer space.

"Musk," which premiered at the Venice Film Festival, seeks to reframe the story of the world's richest man whose stated ambitions include colonising Mars, transitioning the planet to sustainable energy and protecting free speech, laying bare the "unreality of his narrative," Oscar-winning documentarian Alex Gibney said.

"I wanted to understand what game he is playing," says director Gibney at the start of the film about the man long considered a rule-breaking genius whose erratic behaviour and shift to right-wing politics has alienated -- and confused -- many.

Gibney said Musk's story was "oddly familiar" to him, having treated other larger-than-life characters in past films, from the executives behind the Enron scandal to former Theranos boss Elizabeth Holmes.