The 12-hour cutoff for finishing the 20-plus mile loop of the notoriously difficult Barkley Marathons trail race was quickly approaching, and still there were no signs of professional ultrarunner Michael Wardian.

A veteran of extreme races around the world, the 42-year-old Arlington resident has completed the Marathon des Sables — 156 miles over six days under the searing Sahara Desert sun, among other footraces dubbed the toughest in the world. Earlier this year, Wardian averaged 2:45:56 per marathon to win the World Marathon Challenge, a race featuring seven marathons on seven continents in seven days.

But even Wardian was unable to finish one of the five Barkley Marathons loops earlier this month in the allotted time after getting lost.

“It’s probably one of the most difficult races I’ve ever done,” Wardian said in a phone interview. “So many factors are out of your control.”

In the end, only one of the 40 participants this year — 32-year-old John Kelly of Rockville, Md. — finished the course at Frozen Head State Park in eastern Tennessee under the 60-hour time limit, running an impressive 59:30:53. Canadian endurance runner Gary Robbins was six seconds above the cutoff time but would’ve been disqualified anyway because he finished from the wrong direction.

Over the years, the punishing race has become well-known in the ultrarunning community as one of the toughest in the world and the 2012 edition was the subject of the 2014 documentary film, “The Barkley Marathons: The Race That Eats Its Young.”

The unusual event has been clouded in mystique, much of it due to its chain-smoking, eccentric co-founder, Gary “Lazarus Lake” Cantrell. No official website for the race exists and entry applications are not public. Instead, Cantrell — known simply as “Laz” to most — sends out forms to those who are selected. The application fee is $1.60 and sometimes an item of clothing for Cantrell. (This year it was a pack of white socks.)

“He’s definitely a character,” Kelly said. “He has this persona that he comes off as a sadist that’s out to torture people and watch them fail, but he loves nothing more than to watch people succeed.”

The race itself winds through the mountains on an unmarked course and includes a 12,000-feet climb and descent per loop. Runners are given a map beforehand and can use a compass but GPS is not allowed. There are no timing chips and you can only take what you can carry on your back. To ensure the course was covered, competitors must rip pages of out of books along the way that correspond with their bid number and hand them to Cantrell. Weather is often unpredictable and runners this year had the extra challenge of navigating through dense fog throughout the first few hours after the 1:42 a.m. start time. (Start time varies year to year.)

“If you’re going to face a real challenge, it has to be a real challenge,” Cantrell says in the documentary. “You can’t accomplish anything without the possibility of failure.”

Only 15 runners have completed the the full, five-loop race since it began in 1986, with Kelly, a Tennessee native, being the latest. Kelly had attempted Barkley Marathons twice before, dropping out before the end each time due to exhaustion.

“This was without a doubt the toughest event I’ve ever done and I don’t expect that I’ll do any that are any tougher,” Kelly said in a phone interview shortly after his emotional victory. “It’s designed to push you to your mental and physical limits and it definitely did that.”

Kelly didn’t know much about the race growing up, even though he lived on his family’s farm right across the street from the course. He figured it was just something a few people did each year and didn’t think much of it. There wasn’t a big running community in Tennessee anyway, he thought.

But the Barkley Marathons drew a spirited, offbeat group of runners each year. Cantrell had the idea for the race when he learned that James Earl Ray, the man who assassinated Martin Luther King Jr., had only covered eight miles in the mountains after escaping from Brushy Mountain State Penitentiary. Ray had been in the woods for 55 hours. Cantrell thought to himself that he could run at least 100 miles in the same amount of the time.

The race, named after Cantrell’s friend Barry Barkley, was born and it was through these same mountains and trails that Kelly pushed himself to the limits on a cold and rainy April weekend. Kelly, who said a mountain in Frozen Head is named after his family, credited his familiarity with the course for his success.

“My family farm has been there for 200 years,” said Kelly, who now works at a startup company in Washington. “That’s really why this particular race means so much to me.”

Kelly and Robbins worked together for the first four loops but rules stipulated that they go separate directions for the final 20-plus miles. Kelly hobbled through the brutal, rugged terrain, filled with brier patches and his mind began to shut down by the time he touched the yellow gate to signify the merciful end.

He felt heartbroken for Robbins, and was severely sleep-deprived after only napping for about an hour or so in an 80-hour stretch. But the seven-day-a-week training since January and sacrifices he made were worth it for this moment: Kelly was a Barkley Marathons finisher.

“Really what Barkley’s about is discovering what your limits are,” he said. “There’s an extreme joy that comes with high probability of failure. If you’re going out expected to win, that’s cool, but when you accomplish something where the chances are very low that you’ll succeed, it’s really incredible.”