Doodling at work made Roger Hargreaves a multi-millionaire. The advertising executive drew cartoon characters in idle moments, which evolved into the Mr Men -- Mr Tickle, Mr Greedy and many more.
But Hargreaves never thought to create Mr Doodle. That manic persona sprang from the perfervid brain of art student Sam Cox, who had been doodling obsessively throughout his teens, up to 15 hours a day.
Mr Doodle, though he looked like a bundle of fun in his white suit and hat covered in squiggles, was not the benign Mr Man character he seemed at first.
His demented extrovert personality took over Sam's life, enabling him to make a small fortune in the art world but gradually shredding his sanity, until he was sectioned for his own safety in a psychiatric hospital.
This two-hour documentary, directed with sensitivity but also humour by Jaimie D'Cruz and Ed Perkins, depicted the stages of Sam's psychotic breakdown, which seemed to be building up in waves for several years.
Mental health, no longer the taboo subject of a decade ago, is now frequently discussed on TV, but it's rare to see the development of such severe illness shown so clearly.
The Trouble With Mr Doodle deserves to join the case histories of Oliver Sacks, who wrote up his patients' symptoms in a series of bestselling books, as a model of psychiatric study.
Sam has been fortunate to have a close and loving family to sustain him.
His compulsion to doodle over every available surface was so extreme that he fantasised about covering the entire planet in his artwork, and then zooming off in a rocket ship to discover new worlds to daub with jaunty graffiti.
Though no one was interested when he tried to sell individual pages of doodles at £1 a time, his fortunes changed after a Hong Kong art dealer began marketing his work to the cartoon-crazy Japanese.
One sprawling canvas sold for $1m (£730,000), enabling Sam to buy a large, secluded property...which he then proceeded to cover in doodles.
The documentary began at the moment Sam, filmed by his Ukrainian fiancee, Alena, explored the house after it had been stripped of all its cupboards and carpets, with all the walls, floors and ceilings painted bright white. Then, he got his marker pens out...
His breakdown occurred halfway through the project. Incredibly, after he left hospital, he returned to the house and finished every inch of doodling.
Loyal Alena never stopped supporting him, and the one genuinely happy moment in this portrait of fraught, hyper-intense jollity came at the end when their first child was born.
But weighed against that were the interviews with Sam, who seemed deeply anxious to be facing the camera and whose face was sometimes a vacant mask.
These silent close-ups were a reminder that there's so much we simply don't understand about mental illness.