Athletes have long been segregated on the basis of sex. But what happens to the athletes whose physiological traits that distinguish them as female or male don’t match their gender identity? In her first major public appearance since coming out as transgender, Caitlyn Jenner used her acceptance speech for the ESPY's Arthur Ashe Courage Award to talk about her life as an athlete and a transgendered woman.

By definition, transgender is an “umbrella term” that is “used to describe anyone whose identity or behaviour falls outside stereotypical gender norms. More narrowly defined, it refers to individuals whose gender identity does not match their assigned birth gender. Being transgender does not imply any specific sexual orientation (attraction to people of a specific gender). Therefore, transgender people may additionally identify as straight, gay, lesbian or bisexual.”

In a system that segregates athletic competition by sex for reasons of “fairness”, where do transgender athletes fit? The International Olympic Committee (IOC) settled the issue of transgender athletes in 2004, when they released the rules to compete. The IOC rules boil down to three basic points. A transgender athlete must have had gender reassignment surgery, they must have legal recognition of their assigned gender and they must have at least two years of hormone therapy. Given these conditions, the IOC does not consider being transgender an unfair advantage. In 2011 the NCAA instituted somewhat less stringent guidelines, they do not require surgery, and they require only one year on testosterone suppression for male-to-female transgender athletes.

Unfortunately, there are detractors (I’m putting it nicely) who feel Jenner was not deserving of the award and who do not seem to understand why ESPN created the award to begin with. Named after Arthur Ashe, the first (and so far only) African-American male tennis player to win singles titles at Wimbledon, the U.S. Open or Australian Open, ESPN created the award to honour and promote his legacy. Ashe died of AIDS-related pneumonia in 1993. The award recognizes those “possessing strength in the face of adversity, courage in the face of peril and the willingness to stand up for their beliefs no matter what the cost”. While Caitlyn Jenner remains in the spotlight, here's a look at the Top 15 Transgender Athletes who have broken down cultural barriers over the years.

15 Balian Buschbaum

Buschbaum competed for Germany in the pole vault before undergoing gender reassignment, at his retirement in 2007 he ranked 10th on the all-time pole vault performer list. In January 2008, Buschbaum announced that his new first name was "Balian", after the blacksmith in the movie Kingdom of Heaven, and that he would undergo gender reassignment surgery later that year. After the surgery, he said, “Courage is the road to freedom. I woke up in complete freedom today. The sky is wide open.”

14 Erik Schinegger

Erik Schinegger is a world champion skier. Previously known as Erika, IOC medical tests determined that Schinegger was male, which led to his decision to live as a man. Erika was the world champion women's downhill skier in 1966 and was preparing for the 1968 Olympics when IOC medical tests determined Schinegger was male (with internal male sex organs) and disqualified Schinegger. He talked about his transition in his autobiography, My Victory over Myself: The Man Who Became a Female World Champion.

13 Andreas Krieger

Andreas Krieger was a German shot putter who competed as a woman on the East German athletics team. Born “Heidi”, Krieger was given anabolic steroids by coaches from a very young age without his knowledge. So masculinized by the drugs his coaches gave him, Krieger later chose to become a man undergoing a sex-change operation to become Andreas Krieger. Krieger retired from the sport in 1990 and underwent sex reassignment surgery in 1997. He has publicly said that he wishes he hadn't been drugged so that he could have discovered for himself what his gender preference was.

12 Chloe Anderson

Chloe Anderson plays women's volleyball at Santa Ana College in California. In fact she is the first transgender athlete in Santa Ana College.

In an interview with The Orange County Register, Anderson addressed the backlash she's received from some female college athletes. “People who say male-to-female trans athletes have a physical advantage have never taken hormones. It’s one thing to learn about it in biology class but another thing to live it."

11 Keelin Godsey

Keelin Godsey is a 16-time All-American in track and field, a two-time national champion, and holds the Division III national record in the hammer throw. Not to mention, he is the first openly transgender contender for the U.S. Olympic team. Godsey, has publicly identified as a male since 2005, competes as a female in the female division.

10 Jaiyah Saelua

Jaiyah Saelua was the first transgender national soccer player to compete in a men's FIFA World Cup qualifier for American Samoa in 2011. Saelua identifies as “Fa'afafine”, a person in traditional Samoan culture born biologically male but embodying both masculine and feminine gender traits. In an open letter to her Samoan community, Saeula wrote:

"Fa’afafine is the third gender specific to the Samoan culture, but the stereotypes associated with fa’afafine are mostly positive – a perspective that western cultures are freshly adapting to…A million transgender women can be visible in their societies and it truly helps when those women are well-known (i.e.: Janet Mock, Lavern Cox, Carmen Carrera, Caitlyn Jenner), but change comes from society members who do not understand or tolerate. They are the target."

9 Kye Allums

Kye Allums became the first openly trans athlete in NCAA Division 1, the top level of college athletics, when he played on the women's team at George Washington University in 2010. Allums started identifying as a male during his sophomore year and is now a 25-year-old activist, transgender advocate, public speaker, artist, and mentor to LGBT youth. When asked by Time magazine how he decided he was ready to tell people he was transgendered Allums recalled "Playing on a sports team, you become very close. These girls were like my sisters and having them refer to me using female pronouns every single second of the day and not knowing how that made me feel, I couldn’t keep playing like that."

8 Lana Lawless

Born male, Lana Lawless underwent gender reassignment surgery in September 2005.

When Lawless, a retired police officer, won the 2009 Long Drivers of America title, the organization quickly changed their rules stating that female participants must have been "female at birth" to compete. The LPGA removed this requirement after Lawless sued for the right to compete in 2010. She released a statement to help clearly define her position after filing the lawsuit.

"I am, in all respects, legally, and physically female. The state of California recognizes me as such and the LPGA should not be permitted to come into California and blatantly violate my rights. I just want to have the same opportunity to play professional golf as any other woman."

In May, 2011, Lawless officially dropped her lawsuit against the LGA, who released the following statement. “The Ladies Professional Golf Association (LPGA) expresses its appreciation to Lana Lawless for raising the issue of transgender participation in its tournaments and other professional activities. Both Ms. Lawless and the LPGA are pleased that the litigation initiated by Ms. Lawless has been resolved in a satisfactory way, and applaud the LPGA members who voted overwhelmingly to remove the ‘female at birth’ provision from its by-laws.”

7 Chris Mosier

In 2015 Chris Mosier won a spot on Team USA in the men's sprint duathlon, becoming the first trans athlete to join a U.S. national team that matches his gender identity, rather than the gender assigned him at birth. He is the founder of TransAthlete.com, a site dedicated to educating and helping trans athletes, and the executive director of GO! Athletes, a support network for LGBT athletes. Mosier began competing in triathlon in 2009 as a female and competed in his first race as a male in 2010 when he legally changed his name, and then began to receive testosterone injections.

"When I was considering transition, I didn't see any trans men who were athletes," he told The Advocate. "I didn't know it was possible to continue to compete through transition, and I thought I would go from competitive to middle-of-the-pack in races. But the opposite has been true. I've gotten more and more competitive in the male age group, working toward the elite level. My hope is that athletes who are questioning their gender identity can see me and hear my story and know they don't have to give up their identity as an athlete to live authentically."

Mosier will represent the U.S. in the 2016 World Championship duathlon in Spain.

6 Dr. Bobbi Lancaster

Dr. Bobbi Lancaster is a transgender golfer and a successful and well-regarded physician in Arizona. Lancater grew up in Canada as she enjoyed amateur golf success. Bobbi rekindled her passion for the game after she had gender-reassignment surgery to become Bobbi Lancaster in 2010. Only three years after the LPGA’s historic vote, Lancaster was the first transgender golfer to take part in LPGA Symetra Tour.

5 Caster Semenya

One of the most famous transgender athletes internationally is Caster Semenya. In 2009 after winning gold in the women’s 800 meters the IAAF began receiving e-mails from people who had doubts about Semenya’s gender because of her “masculine look” and incredible speed. Tests were ordered amidst accusations and leaked results showed that Semenya has no ovaries or a uterus. The IAAF will not confirm or deny whether the leaked results are correct. If the results are true, Semenya is intersex, and not transgender, as she is rumored to possess both male and female genitalia.

Although Semenya is able to compete; the IAAF struggles with how to define a person as male or female.

4 Fallon Fox

Fallon Fox is the first openly transgender athlete in the history of MMA (mixed martial arts). After a stint in the military, Fox flew all alone to Thailand for “gender reassignment surgery” in 2006. She was forced to come out publicly in 2013 after a reporter indicated he knew she was transgender. Since then there has been considerable controversy over whether or not Fox possesses an advantage over other female fighters.

3 Mianne Bagger

In 2004, by playing in the Women's Australian Open, Mianne Bagger became the first openly transitioned woman to play in a professional golf tournament. A current professional on the Australian Ladies Professional Golf Tour, Bagger had gender-reassignment surgery in 1995. Prior to Caitlyn Jenner’s coming out, many saw Bagger as the most prominent transgender athlete in professional sports.

2 Dr. Renee Richards

While she didn't dominate the tennis world, Renee Richards helped pave the way for trans athletes like Caster Semenya, Kye Allums, and Fallon Fox to compete in their chosen sports.

Dr. Richard Raskind was a pro tennis player and a renowned eye surgeon, but in 1975, after a highly publicized sex reassignment operation, Renee Richards emerged. In a court case that would act as a landmark decision in favor of transgender rights, the New York Supreme Court ruled in favor of Richards' right to compete as a woman after she was formerly barred from playing professionally by the United States Tennis Association.

1 Caitlyn Jenner

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Multiple publications have described Jenner as the most famous openly transgender person in the world since she came out in 2015.

Once dubbed “the greatest athlete in the world”, Caitlyn Jenner is more recently recognized as the quirky Kardashian of reality TV. A gold medal Olympic athlete, Jenner was one of the first people to land a spot on the front of a Wheaties box after dominating the decathlon at the 1976 Games in Montreal. Jenner became an American hero in such a way that only an athlete can.

After months of speculation Jenner officially identified as a woman, appearing on the June 2015 Vanity Fair cover as Caitlyn. In April, 2015 in an interview with ABC’s Diane Sawyer, Caitlyn Jenner came out as a transgender woman, stating "for all intents and purposes, I am a woman."