Michael Cullen went from sleeping rough in Liverpool to raising £1m by doing charity walks in all weathers in just his swimming trunks. His story is now being celebrated in a stage musical.
Just as Clark Kent turns into Superman when he changes into his famous red underpants, Michael Cullen transforms into Speedo Mick when he pulls on his tight blue trunks.
"I got a little inkling of what Superman feels like when he puts his knickers on," Cullen laughs.
"I do feel different when I'm in my Speedos. Something happens. There's a change. I get a little bit more fearless."
Speedo Mick doesn't have Superman's tights and cape - just a pair of walking boots and, if it's cold, an Everton FC scarf and woolly hat.
He has criss-crossed the British Isles bare-chested for charity come rain, shine or snow. His most extreme challenge was walking between, and up, the tallest mountains in England, Scotland in Wales in mid-winter.
"Minus 18 at the top of Ben Nevis. I walked to the top of it and survived it. I never got hypothermia," he marvels.
"So something happens when I put my Speedos on. I get a completely different frame of mind. I'm just so determined to get through the day without putting my clothes on."