A man running through the snow while pulling a tire in Wellesley

Until a man is twenty-five, he still thinks, every so often, that under the right circumstances he could be the baddest motherfucker in the world. "If I moved to a martial-arts monastery in China and studied real hard for ten years. If my family was wiped out by Colombian drug dealers and I swore myself to revenge. If I got a fatal disease, had one year to live, and devoted it to wiping out street crime. If I just dropped out and devoted my life to being bad."
Hiro used to feel this way, too, but then he ran into [the dude running through Wellesley dragging a tire through the snow]. In a way, this was liberating. He no longer has to worry about being the baddest motherfucker in the world. The position is taken.

-- Neal Stephenson, Snow Crash

I'm convinced that this is ultra-runner and obstacle racer Junyong Pak from the Beverly area. When he was profiled in Runner's World a while back, a lot of the attention focused on his love of winter training and habit of pulling a tire around.

Some highlights:

he quickly strips down to his shorts and a gray tank top, scrunches down to his knees and elbows, and begins army crawling through the slush with the kind of methodical calmness you'd see in a yoga studio.

he worked out at night, cramming two sessions into one, beginning as late as 10 p.m., when he was extra tired and it was invariably "freezing cold and raining or snowing or sleeting." He described these sessions as his favorite because he knew they separated him from everyone else. On return he'd come home to a house with no heat—part of an acclimatizing plan to make him cold-proof. "When you can turn the heat off in the house," he'd reflect, "and be comfortable at, like, 45 degrees—and when everybody else says, 'You're crazy, turn the damn heat on!'—you begin to sense that you have something others don't."

As he attacked Lynch Park with lap upon lap of swims, sand rolls, and punishing hill repeats, he fortified himself with canned peach chunks and halved pears he bought at markdown. He often dragged a rope-leashed BFGoodrich tire behind him to simulate climbing bigger and longer hills.

Closer to home, his unorthodox training had landed him in a bit of trouble. In January, he'd been stopped from dragging his tire during a weekly fun run called the Danvers 5-K when complaints mounted and a town-council meeting addressed the matter. "The only issue I have," an irked council member said, "is the guy dragging the tire."