In the stagnant country of his little bedroom, on the island of his gigantic bed, with two curtains sewn together to clothe his body, Paul Mason decided that he didn't want to die. Three years had seeped in and out of the room, with his head at the same angles, the mass of him pooling outward, the banal sensation of the air-conditioning breathing onto his urine sores. By then Mason had been dubbed the world's fattest man, perhaps the most ridiculed person in the United Kingdom, trapped on a 10-foot mattress, everything he'd ever collected on shelves within arm's reach. He was also weary of his appetites; he no longer wanted to consume his daily intake of nearly 20,000 calories. He was exhausted of wondering what it might be like outside his house.

He wanted out of his skin, and skin was all that he'd become. He had given up on losing weight naturally. His breakfast was the meal of ten people—a pack of bacon and a pack of sausages and countless eggs, and his snacks were 40 bags of potato chips and 20 chocolate bars a day. An intercom system on his front door allowed restaurants to deliver food to his bedside, entering his little flat through the doors and hallways specially widened by England's National Health Service. He wore a little white towel draped over his privates. At his heaviest he'd weighed 20 pounds shy of 1,000.

He knew that bariatric surgery had a good chance of killing him, just as it could save him. The procedure, he understood, would shrink his stomach from the size of a melon to the size of an egg, bypass much of his small intestine, and give him a 50 percent chance at a new life. The other 50 percent meant a possible heart attack or blood clot, a burst vessel, catastrophic organ failure—a complication that would snuff him out before he even awoke from the operation. But without the surgery he was dead anyway.

And so on a freezing day in the winter of 2010, five paramedics in yellow suits wheeled Mason out of his home on the bed where he lived. Using a motorized winch, they hoisted his extra-wide reinforced stretcher into the back of the supersized ambulance that the Suffolk branch of the NHS had scoured all of Great Britain to find. (A helicopter, which had been considered, didn't have a door wide enough.)

The ambulance drove south, followed by photographers trying to snap pictures of the human being the tabloids had dubbed "Man Mountain." He watched the traffic out the back windows. How bizarre, he thought—he hadn't remembered that cars could go so fast.

Paul Mason, bedridden. Paul Nixon Photography, Ipswich UK

The logistics of getting him into surgery were unprecedented. Engineers had realized before he arrived that the operating room probably wouldn't be sturdy enough to hold him. After consulting blueprints, they ultimately installed metal supports beneath the floor. Then doctors had to make a scary guess about how much anesthetic to pump into their patient. He needed much more than a normal person; the customary amount would merely dissolve in his body. But too much could mean death.

He was all too familiar with that precarious balance. In 2008, he had tried to commit suicide by taking enough codeine to kill two people, but he'd woken up the next morning with only a headache—his body had absorbed it all. Now he'd had a change of heart.His surgeon, Shaw Somers, was something of a celebrity in Britain. He had appeared on a TV show called Fat Doctor, and had operated on thousands of obese patients. When he first visited Mason to assess whether he could withstand the surgery, Somers stood over his bed. With his bare hands, he pushed around on the mound of Mason's torso, lifting the folds that caregivers had spent hours rubbing with medicinal cream, revealing buried, luminescent skin. When he was done, Somers asked Mason if he would be willing to die in order to lose weight. Mason began to bellow and sob. Yes, he told Somers. He was willing.

On the day of his surgery—after first spending two weeks on a milk diet in order to lose as much weight as possible beforehand—Mason lay on a new surgical bed, the largest available, though his skin still dangled off the side. Somers and his team set about performing a keyhole gastric bypass, which required sticking five ports into small incisions patterned out on Mason's abdomen. Blood trickled down his stomach from each hole where the ports went. Somers manipulated his surgical instruments through the ports, using shears and stitching instruments to cut around Mason's stomach fat. Mason was asleep, a breathing mask covering his face. Though most of his internal organs were blanketed in a thick yellow layer of fat, his heart looked amazingly healthy.

The surgery took two hours. Somers wore a surgical cap patterned with an apropos design: rolling dice.

He wasn't always so heavy; he wasn't always so big. But Mason was taller than everyone else in school. He remembers being nearly six feet tall when he was nine years old, tall and awkward and shy. When he walked to class the other boys would climb on his back and try and tackle him to the ground.

He found little comfort at home. He was terrified of his father, a martinet who spent years in the army and military police. Mason always finished the dinner his mum prepared—his father wouldn't let him up from the table if he didn't clean his plate.

Mason, his parents, his two sisters, and an aunt lived in a middle-class house in the town of Ipswich, about 75 miles northeast of London. There weren't enough beds in the house, so he shared one with his aunt. He says she would come home drunk and climb in the bed with her breath on his neck and touch him, and that lasted for three years, which is something he didn't tell anyone until he sought counseling in 2008 when he weighed well over 900 pounds.

There were some things, at least, that made him happy. Like riding his bicycle around Ipswich. He had a paper route in the mornings and attached long handlebars to his bike from which he would hang his satchel of papers. He played percussion in the Salvation Army Church band. He sat in his bedroom, drawing hot rod cars in pencil on construction paper that he would cut out and tape to his chair.

His two best childhood mates were Pum and Joan. They lived in an apple tree, and no one else could see them. Mason looked out at the tree from the big sash windows in his room that opened up toward the garden, so he could always keep an eye on his imaginary friends. "Pum and Joan were two girls," he told me when I began getting to know him last year. "Just two honest schoolgirls. Normal girls, who listened to me when I was sulking most of the time." He climbed the tree and sat up behind the branches with them for hours.