Jenner entered therapy in the 1980s and planned to transition before she was 40, but eventually decided she couldn't go through with it.
She soon met Kris Kardashian and became step-father to Kourtney, Kim and Khloe. They had two more daughters together, Kylie and Kendall.
The marriage broke down, and Jenner once again considered transitioning.
"Now things were different," Jenner says, "and what a great opportunity to make a genuine contribution to understanding in society when you're playing in the fourth quarter of life."
In 2015, Jenner appeared on the front cover of Vanity Fair as a transgender woman, and was awarded with the Arthur Ashe courage award at the ESPY awards in America, the equivalent of the Oscars for sports.
She has been living as a woman for five years now.
Asked what her greatest achievement has been, Jenner says: "I would have to put my identity as higher. It was tougher to do. I trained 12 years for the Olympic Games. I trained 65 years to transition in 2015.
"It was less accepted. Everyone loved the Games. A lot of people when they see you transition hate your guts. Look at the quotes on Instagram. By far that was a lot more difficult.
"Being gender dysphoric and dyslexic- that's what made me down the line. When I got into sports, it became more important for me to succeed at sports and work hard at sports because of all these issues.
"I look at a lot of people who are successful, and then you look back on their lives and it's 'Oh my God, this is what you were struggling with when you were younger'.
"I don't have to sneak around anymore. I don't have to have two suitcases, one for him one for her.
"I'm glad I had all those issues. They say success is not measured by heights obtained but by obstacles overcome."
Jenner has faced criticism from trans-rights activists, external for her politics and support of US President Donald Trump.
She admits that the backlash "does hurt" and that she does read some of the social media abuse, but "wants all the other trans people out there to use their platform".
On her own trans campaigning, she adds: "Has it been easy? Not even close. I've raised about $2.6m and given it away to trans organisations. A lot of them are extraordinarily appreciative of it. On the other hand sometimes they're having their big fundraiser and say 'Oh please don't show up - you're too controversial'."
With the Tokyo 2020 Olympics on the horizon, a number of high-profile female athletes have said transgender athletes should not be allowed to compete in female competitions, arguing women born biological male retain a competitive advantage in some sport - and calling for more research from sport's governing bodies into the issue.
Trans athletes claim they should not be blocked from participating in sport, and some have claimed the science around physical benefits is still unclear.
The current IOC guidelines state that transgender women must suppress testosterone levels for at least 12 months before competition - although they are working on new guidance to "strike the right balance between fair and equal competition and non-discrimination".
Jenner added: "I think they should do exactly what they are doing. The International Olympic Committee is the only organisation who has taken this issue seriously for many many years.
"Everyone deserves a right to be able to compete, and so they started coming up with hormone levels so now trans people can compete. Nobody has made an Olympic team yet.
"I think the most important thing is people that are different, people that are dealing with trans issues and stuff like that- I think they deserve an opportunity to play sports. Sports was very very good to me. We should not deny them of that opportunity. But also we should look at it closely and almost deal with it on an individual basis. But the Olympic committee is doing a good job."
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