By Steve Keating

TORONTO (Reuters) - Clara Hughes has already won her biggest battle. A rebel who found a cause, she is the only athlete to win multiple medals at both the Winter and Summer Games.

The 39-year-old was once a troubled teenager, now she is an inspiration to millions of Canadians, finding success in speedskating, cycling and life.

She already has six Olympic medals, equaling her speed skating teammate Cindy Klassen as Canada's most successful Olympian, but may not be finished yet after booking her place in the team for London.

"I have no idea what lies ahead after London," she told Reuters. "If it continues, it continues, if it stops I can call it a pretty good career.

"As an older athlete realising this could be the last chance I have to live this challenge, this opportunity to achieve something that means something to me."

At London, Hughes will be competing at her sixth Olympics, three Summer and three Winter, in 16 years. She won medals at four of her five previous Games.

She collected two bronze medals in cycling at the 1996 Atlanta Olympics, and four medals in speedskating, including gold in the 5,000 meters at the 2006 Turin Games.

She missed the last two Summer Olympics after giving up cycling but decided to make a comeback and qualified for London.

"I'm thrilled beyond belief to be on this Olympic team, just to have the chance, the honor, to earn my spot for a sixth time in my life is something I don't take for granted," she said.

"It's something so humbling, so special...I feel completely inspired by this opportunity. That hasn't changed, it hasn't dulled one bit.

Olympic fame certainly did not appear to be in Hughes' future when she was growing up in Winnipeg as a rebellious teen.

A runaway and pack a day smoker, Hughes skipped school, drank alcohol and dabbled in drugs, the only record she seemed destined for was a police record.

Her life changed when she was 16 and watching television. She saw a profile of Canadian speed skating great Gaetan Boucher and was instantly hooked.

Her fascination with speed skating was enough to set her life on a new course but it was soon replaced by another athletic pursuit, trading in her blades for a bike.

In Atlanta, she finished third in the road race and third in the time-trial. She also rode at Sydney in 2000 but did not win a medal so returned to her first sporting love.

At Salt Lake in 2002, she won a bronze in the 5000m, becoming only the fifth athlete to win medals at the both the Summer and Winter Games.

In Turin, she became the first multiple medalist, winning gold in the 5000m and silver in the team pursuit. She also won a bronze at Vancouver in 2010 and was given the ultimate honor of carrying her nation's flag.

She has also been awarded a star on Canada's Walk of Fame and named an officer of the Order of Canada for her work outside of sport. When she won her gold medal in Turin, she donated $10,000 to the humanitarian group Right To Play.

And after having battled depression herself, she become an advocate and spokesperson in a campaign to combat the stigma that surrounds mental illness by telling people about her own struggles and how she overcame them.

"After my first Olympics, I ended up in a state of depression from pushing myself for so long, so hard beyond any reasonable way a human being should be pushed," she said.

"Leading a focused, meticulously planned out life that revolves around peak performance. I think in some ways I have mastered that."

(Editing by Julian Linden)