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Mimi was born "Mark" in Waterloo, Iowa, but grew up in Oelwein, Iowa. As a boy, she recalls feeling "uncomfortable in her body," and had the "most difficult time" in her physical education class because, she says, "I didn't fit in at all."
After undergoing some sex-reassignment surgeries (due to stipulations in employment contracts, Marks hasn't had complete sexual reassignment), Marks became Mimi. According to Trantasia , a transsexual beauty pageant documentary, she has lived as a woman since she was 21 years old. Marks started performing in Milwaukee at a club called Dance, Dance, Dance with help from an Australian performer, Holly Brown. Marks says that, for transwomen in Chicago, the test of whether they can pass as women is to appear in public at Wrigley Field, home of the Chicago Cubs: “"If you could walk through Wrigley-ville, like, during a Cubs game and not get 'spooked,' and not have anybody call you out, you were like the 'girl-iest' girl, you made it. I called [a friend] and said, 'I am at a Cubs game on first base, eleventh row. I made it. I'm a girl!'" 
In 1986, Marks won her first pageant title: Ms. Waterloo 1986. She has also won Miss International Queen, Pattaya, Thailand; The World's Most Beautiful Transsexual Contest, Las Vegas, Nevada, USA; and Miss Continental, Chicago, Illinois, USA.
Marks is reported to have been the first ever openly transsexual runway model, working for the Ford Modeling agency.