A difficult birth left Andrew Tomlinson with a brain injury which made his chances of ever walking slim.
But more than 30 years later, he believes he is the first runner with cerebral palsy to complete all six of the world's major marathons.
On Sunday, the 40-year-old from Glasgow crossed the London Marathon finish line in under four hours.
He has previously completed races in New York, Chicago, Tokyo, Boston and Berlin.
Andrew said building up to the London race had taken three years of his life.
"At the end I was fighting against all the emotions - pride, joy, finishing ... but also sadness too, because it's finished.
"I wanted to go back to the start."
Andrew has hypertonic cerebral palsy, which means he suffers from tightening muscles and regular spasms.
It affects his the mobility down the left hand side of his body and means he walks with a visible limp and has slurred speech.
He receives regular treatment as symptoms can flare up, causing him severe discomfort.
"It's one of the worst pains," he says.
He says keeping active also helps control some of the pain, making it more bearable to live with the condition.
"Running also hurts but I've noticed that the more I run the less the cerebral palsy hurts, so it's actually helping me," he says.
There are about 16,000 people with cerebral palsy in the UK, and it affects everyone differently.
Along with the physical impact of the condition, Andrew has also suffered socially, which is why he made the decision to take up running.
He says cerebral palsy can often isolate him from others. In 2019 he realised that he'd got himself into a rut and that something had to change.
"I'd come home from work and play a games console by myself and one day I thought I really have to challenge this, cerebral palsy was winning.
"I spoke to a friend who suggested I try a marathon. I thought, I don't even know if I'll manage a 10k, let alone a marathon."
Marathon 'miracle'
Within six months, Andrew had travelled to Berlin to complete his first world major marathon. The next year he joined his local road running club, which he says enhanced his life.
"I now have a hobby and a social life," he adds.
His mum Linda says that the fact Andrew is able to walk, let alone run marathons, is a miracle after a difficult birth left him with damage to his brain.
"He had lack of oxygen to the brain but we didn't realise at first," she says.
"When he was one we noticed he wasn't using the left hand side of his body. I took him to the doctor who referred him to a specialist.
"It was then we were told he has cerebral palsy and that he might never walk."
'A true inspiration'
Linda took medical advice and Andrew attended physiotherapy at Glasgow's Yorkhill hospital for sick children.
Within two years he took his first steps.
"He tripped up and fell often, even today he struggles - but when he does fall he gets straight back up again.
"But running seems to have the opposite effect. When he runs he relaxes, it's like he's not got cerebral palsy."
Linda says she worries about Andrew on his solo travels around the world completing marathons, but knows he's doing what he loves.
"He puts an awful lot of work in, he never complains and he tries so hard to keep himself mobile.