The actor/director was sent a manuscript of the book after briefly meeting the author once in 1979, and he was charmed by the story about an oddball former agent.

"This is a book that came to me in a kind of mysterious way...," Penn told comedian Bill Maher during an appearance on his Real Time show. "He's someone I met once in 1979... who had the address of my mother. Then some time in early May this year I got a manuscript... I think I was the only celebrity he'd ever met, so after writing this book he thought of this guy he met in 1979.

"I read it and what I was reading was in essence the book that I would have written if I was writing a book... My suspicion is that much of what's in it might be true but expose highly illegal activities on his part, and so he's made it a fiction."

Sean reveals the tale "quite clearly" features a character modelled after controversial U.S. presidential candidate Donald Trump, and he was blown away with how timely the story was.

"So often at this time when you're watching the news you just feel that the reporter or the pundit should not be continuing to speak but actually running to pull the fire alarm and say, 'What the hell is happening here?', so this book... I realised that almost everything his character, Bob Honey, is doing and believing and the thought process, was in sync with what I thought... but I was hearing it from a character who's really a sociopath.

"I thought, 'Well, when a sociopath is making more sense than anything we're seeing in mainstream news media, it's time to hear them out'.

"Also the title got me - Bob Honey Who Just Do Stuff - because that's what it's about. He just do stuff."

Penn will be reading the book live at an upcoming event at the Los Angeles County Museum of Art on 6 October (16).