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Mianne Bagger (born 25 December 1966) is a professional golfer from Denmark. In 2004, by playing in the Women's Australian Open, she became the first openly transitioned woman to play in a professional golf tournament. She also became the first trans woman to qualify for the Ladies European Tour in 2004, and the first high-profile transitioned woman to qualify for a professional sports tour since Renee Richards joined the Women's Tennis Association tour during the 1970s.

She has been instrumental in gaining eligibility for transitioned women to compete on professional golf tours. Through her efforts, many professional golf organizations have amended their practices, but the policies generally still constrict rules of gender variance, and view atypically gendered women as something other than women. Bagger caused a media stir in 2004 when she played the Australia Women's Open and had intentions also of joining the Australian Ladies Professional Golf Tour (ALPG Tour). At a tournament in the United States, she met Ty Votaw, the commissioner of the LPGA Tour, who was later questioned about their policies stating "right now, our rule is that they have to be born women." Bagger notes that "they obviously don't consider that I meet that condition." Votaw left the possibility open for that rule to change in the future.

The 2004 ruling by the International Olympic Committee (IOC) regarding transitioned athletes led to a re-examination of rules in many sports. The IOC 2004 Stockholm Consensus, which researchers have criticized as "a measure that polices the traditional gender binary while being disguised as a progressive and inclusive measure," spells out specific requirements for a transitioned athlete. Bagger notes that the USGA policy requires "a signed waiver by the entrant giving complete and unrestricted access to one’s medical records and pre-operative and post-operative psychiatric records" Bagger, along with a few high-profile athletes and a growing number of medical professionals and researchers around the world, continue to lobby the IOC, IAAF, WADA et al. in their approach to embracing transitioned athletes.