[Editors’ Note: If you are having suicidal thoughts, please contact the National Suicide Prevention Lifeline: 1-800-273-8255 (TALK).]

When news broke that Dave Mirra, the most dominant and decorated BMX star in X Games history, had committed suicide at age 41 in his hometown of Greenville, North Carolina, on February 4, his friends thought it was an Internet hoax. A few even texted Mirra to let him in on the joke.

“That’s the last guy you would think, because he’s stronger than you,” says Ben Bostrom, a retired motorcycle racer who was Mirra’s triathlon training partner.

Mirra’s strength and determination were renowned. Driven and intense, he had won 24 X Games medals in two decades of competition, all but one of them in BMX. (He also won a bronze medal in rallycross in 2008.) But he was humorous and sensitive, a devoted family man to his wife, Lauren, and daughters, Madison, 9, and Mackenzie, 8. Friends say it seemed like he had a lot going for him.

“We’ve got a good collage of misfit individuals in our community,” says BMX icon Mat Hoffman, 43. “He was the one who had it the most together out of all of us.”

Recently, the 41-year-old had surprised friends by telling them he was planning a comeback to the sport: he was building a new vert ramp for training; he presented the Number One Rider Award (NORA Cup) at a September BMX awards ceremony in Las Vegas; and he was making arrangements to attend a reunion of older and retired riders in California in March. “Everyone was getting real excited,” says Hoffman.

In the nearly two weeks since his death, some have speculated that head trauma—Mirra, like many BMX riders, took multiple spills over his career—may be to blame for his death. Indeed, those who suffer from Chronic Traumatic Encephalopathy (CTE), the degenerative brain condition currently plaguing football and other sports that involve significant head trauma, often suffer from depression and exhibit impulsive behavior. NFL Hall of Fame linebacker Junior Seau, who in 2012 shot himself in the chest at age 43, had CTE; Greenville Mayor Allen Thomas, who was friends with Mirra, suggested that he might have had it as well. (UPDATE: In late May, Mirra's widow, Lauren, announced that a study of her late husband's brain concluded that he had CTE. The study was coordinated by Dr. Lili-Naz Hazrati, a neuropathologist at the University of Toronto, and the Canadian Concussion Centre. The diagnosis was confirmed by neuropathologists in the U.S. and abroad, according to a release by a Mirra family spokesperson.)

But in more than a half-dozen interviews with friends, colleagues, competitors, and authorities, it became clear Mirra had lost direction, whatever else he may have been suffering from. When he ended his BMX career in 2010, at age 35, he refocused his passion and commitment first on rally car racing, then on a budding interest in triathlons. But several setbacks last year caused his commitment to waver. Famous for his energy and work ethic, Mirra complained of fatigue and confessed that he was feeling down. Alarmed, some friends talked and said they needed to keep an eye on him.

Born in 1974 in Chittenango, New York, near Syracuse, Mirra stormed the BMX scene in 1987 when he was 13. (Even at that young age, he was already sponsored by Haro Bikes.) After dominating riders in his age group with a repertoire of the most advanced tricks, performed with uncanny consistency, he turned pro at 17.

“He had a young cocky persona, but it was done with humor,” recalls Dennis McCoy, 49, who was an established pro when Mirra first arrived on the scene.

At the time, Mat Hoffman was the dominant competitive rider. When he first saw Mirra, he realized that reign was over. “I was like, ‘I better start getting used to getting second,’” he says. “A lot of us specialize in different disciplines in the sport, but Dave could do all of it. He could do big, burly tricks, then lay down the most beautiful finesse on the ground.”

When [Hoffman] first saw Mirra, he realized that reign was over. “I was like, ‘I better start getting used to getting second,’” he says.

Mirra’s career nearly ended just as it was taking off, though. In 1993, when he was 19, he was hit by a drunk driver after leaving a club in Syracuse, fracturing his skull, dislocating his shoulder, and leaving him with a blood clot on his brain. He spent six months off his bike while recovering. In 1995 Mirra had his spleen removed following a slam at an event in Dallas. The injuries didn’t stall his ascent in the sport, though. When ESPN debuted the X Games (then known as the Extreme Games), in Providence, Rhode Island, in 1995, Mirra capitalized on the increased visibility and commercial opportunities for what had been a fringe sport.

“He was exactly what we were looking for in terms of a marketing message about the X Games,” says Chris Stiepock, who spent nearly 20 years working on the X Games for ESPN, and now works at NBC Sports. “He was clean-cut. He was well-spoken. He was obviously very athletic, and he took it seriously.”

With the retirement of skateboarder Tony Hawk in 1999, Mirra emerged as the face of the X Games franchise. In 2000, he became the first BMX rider to land a double backflip in competition, and was soon featured in ads for Burger King and sponsored by Slim Jim and DC Shoe Co., which designed a signature line of shoes for Mirra. His name even graced a video game franchise by Acclaim Entertainment.

Mirra once held the record for most X Games medals by any athlete with 24, including 14 golds (which was broken by skateboarder Bob Bunrquist in 2013). He won the Park and Vert competitions from 1997 to 1999. “Because he was so great, he was his worst critic,” Hoffman says. “Everybody else is praising how amazing he is, and in his mind he’s like that could be better and I’m going to make it better, and he did.”

He earned at least one BMX medal every year from 1995 until 2009, except for 2006. That was the year, while practicing on the Park course at the X Games in Los Angeles, Mirra fell 16 feet from a ramp onto his head, in what he described as his worst crash ever. He spent months recovering after a trip to the ICU. Although he returned to competition and won three more medals, his era of dominance was over. Mirra would never win gold again. In 2010, he missed the X Games while recovering from bacterial meningitis, which his wife, Lauren, said had nearly killed him. (Without a spleen, he was more susceptible to infection.)

He had also begun showing psychological effects from all of his injuries.

“There’s this term called pop-out-itis, whenever you’re going fast at a ramp and your brain switches where you can’t do this, and you jump out to the deck. He did that a couple times, and was like, ‘Man I’m getting this pop-out-itis,’” says Hoffman.

In a 2013 interview for X Games.com, Mirra explained his mindset leading to retirement. “For me, it came down to risk versus reward,” he explained. “My mental stance on it was that I always loved to progress, first and foremost. It was never going to be that fun for me to go on riding on a plateau level and not keep progressing, but by the same token, I got to a point where I really couldn’t take getting injured anymore in the name of progression.”

Rather than show up and fail to place, Mirra simply walked away from his bike. “I don’t really miss it,” he said in the interview.

BMX fans were upset about the abrupt retirement. T.J. Lavin, a BMX medalist who retired in 2010, remembers talking to Mirra about being the object of public ridicule. “People would talk shit about us [on social media and online] and it would hurt our feelings,” Lavin says. “He was very, very, very sensitive, almost to a fault. He would say, ‘Oh, Lavin, I don’t give a shit.’” But when pressed, Mirra would admit that the criticism stung.

There comes a reckoning for every athlete when his skills diminish and his competitive career begins to wane. Faced with life-altering, disorienting decisions, he’s dogged by questions about himself: Who am I now? And where do I go from here?

“It is a big comedown,” says Lavin, whose career ended after he crashed while competing in a 2010 BMX dirt jumping event, sustained bleeding on his brain, and was placed in a medically-induced coma. “You see it with everybody, from baseball to football players and everybody else. They’re not in the pinnacle of their career anymore. It’s a hard pill to swallow.”

Retirement didn’t sit well with Mirra either, who friends say felt adrift without someplace to channel his inner drive. “He was the most fierce competitor I’ve ever known,” says Katie Moses Swope, Mirra’s publicist. As his BMX career wound down, Mirra tried to direct his substantial energies into another X Games sport: rally car racing. At first, he was successful. He won a bronze medal in the event at the 2008 X Games, and joined the Subaru racing team. But he struggled to continue that success. In 2013, he was bounced from Subaru, and joined the Mini team, where he posted fast qualifying times, but was dogged by wrecks and false starts.

Then, in 2012, Mirra watched a friend from Syracuse, Eric Hinman, compete in an Ironman in Lake Placid, New York. He recognized something that was both familiar (he had, after all, made a career riding a bike) and presented a new challenge. Mirra hired a coach and devoted himself to triathlon training in 2012.

“I saw his training, his intense dedication, and decided I needed something to fill a void,” Mirra told Triathlon Magazine Canada about Hinman’s example. In March 2013 he competed at the 70.3-mile Bay Shore Triathlon, in Long Beach, California, placing fourth. “When I called my wife from the finish line I was almost in tears I felt so good,” he told SI.com.

Mirra told XGames.com that he liked the heart and hard work required to get a good result. “I’ve never been a runner,” he said. “I’ve never been a swimmer and I never spent much time on a road bike, but I’m willing to put the work in and I’ve got some big personal goals for next year.”

He competed in the Raleigh Ironman 70.3 but was bogged down with the swim and run. He struggled to finish races in 2013 and switched coaches to improve his swimming. In September of that year, he qualified for the 2014 70.3 World Championship in Mont-Tremblant, Quebec. He finished in 4:36, good for 79th out of more than 300 in his age group.

As he trained, he began talking to Ben Bostrom, a pro motorcycle rider who he had met on the 2014 Race Across America, a 3,000-mile road bike race from the Pacific coast to the Atlantic. When one of Bostrom's teammates got sick in the race and Bostrom had to log more miles, Mirra offered to ride with Bostrom, even though Mirra had just completed his own ride. Their friendship was cemented in the grind of long days on the bike. The two made a pact to qualify for the 2015 Ironman World Championship, in Kona, Hawaii.

“I definitely didn’t have his work ethic,” says Bostrom. When other riders turned their bikes over to mechanics while they ate dinner and rested, Mirra would set to work on his own bike. “I’ve never seen anybody put so much into it.”

Mirra switched coaches again in preparation for a full Ironman’s longer distances (140.6 miles instead of the 70.3-mile half-Ironmans). “This is what scares me about the full distance,” Mirra told Triathlon Canada. “I just change as a person. It’s like a first relationship in high school, where not a second goes by in the day when you’re not thinking about the person.”

Ironman officials had previously offered Mirra a “media” qualifying exemption for the world championship. The same offer had been made to Olympic champion speed skater Apolo Ohno and retired Pittsburgh Steelers receiver Hines Ward, but Mirra turned it down. He wanted to earn his way.

Because both Bostrom and Mirra were 41, and every event has a limit on the number of qualifying slots for Kona in each age group, they registered for separate competitions last year to avoid being in direct competition for a slot. Bostrom competed in Ironman Canada in Whistler, British Columbia, while Mirra signed up for Ironman Lake Placid, both held July 26.

“It is a big comedown,” says T.J. Lavin. “You see it with everybody, from baseball to football players and everybody else. They’re not in the pinnacle of their career anymore. It’s a hard pill to swallow.”

Bostrom battled the conditions—becoming nearly hypothermic. While he crossed the finish line, he did not qualify. Meanwhile, Mirra struggled on the run, finishing in 11 hours, 54 seconds, good for 24th in his age group but not good enough for Kona. After the race, the tone of his Instagram posts was overwhelmingly positive and triumphant. Yet Bostrom heard something else when they caught up by phone. “I could hear the letdown in his voice,” he says, “trying to figure out why he failed. He analyzed it. He broke it down.”

Bostrum said they could train together and try again in 2016. He said they would be stronger. At first, Mirra seemed to agree. In the coming days, however, he changed his mind—he wanted to attempt to earn a world championship slot at Ironman Mont-Tremblant on August 16, less than three weeks after the Lake Placid race. Rest and recovery from an Ironman is measured in months, not weeks. The psychological and physiological toll is depleting. Mirra disregarded that and went at another competition full bore. He completed the 2.4-mile swim in a personal best—one hour, seven minutes—but his legs simply stopped turning during the bike ride, and he did not finish. “Mirra went back for another go in just two weeks,” Bostrom says, “which the body can’t do.”

On September 17, Mirra was in Las Vegas—where both Bostrom and Lavin live—to attend the Number One Rider Award (NORA Cup) ceremony, an annual gathering of the tribe held by Ride BMX magazine. “No one had seen him in a while because he had been in his other worlds,” Hoffman says. “Everybody was so ecstatic that Dave was there. It was more like a Dave reunion than an awards show.”

Mirra stayed at Lavin’s house that week, and the two of them planned to join Bostrom to do some time trials. (Lavin is a triathlon competitor as well.) But the intense training never materialized: they rode bikes only once, and swam once in Bostrom’s pool. “It wasn’t the guy I was used to hearing push me,” says Bostrom. “Instead I was pushing him to try to train.”

One night Mirra replied by text. I’m sorry, Bostrom recalls him saying. I don’t mean to let you down. I just feel really low. I guess it’s just midlife crisis. The next day he sent another text saying he needed to get home to his girls. “He left just like that,” says Bostrom.

Lavin had his own cause for concern. A teetotaler, he had observed Mirra drinking more than usual that week. One night he sat Mirra down at a Starbucks at 4:30 a.m. “I was like, ‘Dave, you’ve developed some bad habits and it’s not a good look’,” Lavin recalls. “I wanted him to focus on being a great dad and a good person.”

One night Mirra replied by text. “I’m sorry,” Ben Bostrom recalls him saying. “I don’t mean to let you down. I just feel really low. I guess it’s just midlife crisis.”

The day Mirra left Las Vegas, Lavin phoned Bostrom. “We’ve got to watch that guy,” he said. “He’s pretty down.”

Both men periodically called to check up on Mirra. “I’m just tired, man,” he told Bostrom on one such phone call. “My body is just tired.”

On the afternoon of Thursday, February 4, Mirra was at home in Greenville visiting a friend across town. “They were making plans to go out again,” Greenville Police Chief Mark Holtzman would explain one day later. Around 4 p.m., Mirra left his friend’s house, climbed into the cab of his truck, which was parked in the driveway, and shot himself with a handgun. He left no suicide note, but Holtzman said a police investigation concluded that “he had been struggling in some areas like [depression].”

After Mirra’s suicide, Bostrom got a call from Jimmie Johnson, the six-time Sprint Cup series champion, and another fitness fanatic. “Have you looked into head injury?” he asked. Bostrom hadn’t, though he had sustained a major blow in a motorcycle crash at Daytona International Speedway. Johnson explained that a football player friend of his had gone just like Mirra. “You guys should look out for each other,” he said.

To Lavin, CTE sounded plausible. “There’s no other explanation for why a guy with everything would do something like that,” he said.

Others were skeptical. Hoffman, who estimates he’s had at least 100 concussions, was among them. “It’s so easy to go, ‘OK, that’s what’s wrong,’” he says about CTE. “I don’t think it’s so simple.”

Many are baffled that a man with so much to look forward to—his wife and daughters, a return to BMX—would give that up. Yet some friends wonder if his failure to reach new goals in new sports may have contributed to that moment. They knew that Mirra's success was due to an abiding drive to achieve more. At 41 years old, though, his days of performing at the highest level were dwindling. Hoffman was even wary about Mirra's return to BMX, though he says the two never discussed it. Hoffman didn't want to add to any pressure Mirra had already put on himself.

"The greatest athletes and artists are their worst critics,” Hoffman says. “The trick is being your worst critic while not driving yourself crazy.”