There are a few reasons Serena Williams could make this list. She’s arguably the most dominant tennis player of all time, with 23 major singles titles, 14 major doubles titles, and four Olympic gold medals to her credit. However, the main reason she’s here is pretty simple: She won a major, at age 35, while pregnant.

She defeated her sister, Venus, in the finals of the 2017 Australian Open. The win was her eighth title in that event and her 23rd major, which broke Steffi Graf’s previous career record. Less than three months later, she revealed that she was 20 weeks pregnant, and the timing of the announcement meant that she was playing in the Australian Open about five weeks after her daughter, Alexis, was conceived.

By any measure, Serena Williams is one of the most elite athletes of the 21st century. She’s won everything there is to win in tennis (in some cases, multiple times), and when she retires, it will be with accolades that may never be repeated by anyone else in her sport. Winning a major while carrying another human being inside of her speaks volumes about not just her talent, but her physical and mental toughness as well.