Happy birthday, Monica Seles! The nine-time Grand Slam singles champion turns 40 today. In 1990, when she was just 16, Seles became the youngest French Open winner, and she went on to win another seven major titles before her 20th birthday. She reached No. 1 in the WTA rankings for the first time in March of 1991. Her dominant career was derailed in 1993 when a Steffi Graf fan stabbed her in the back with a knife during a match, resulting in a two-year hiatus from tennis. Seles returned to competition in 1995 and won the 1996 Australian Open, her final Grand Slam title. While she continued to play until 2003, Seles never regained her dominance. She officially retired in 2008 and has since been inducted into the International Tennis Hall of Fame and has also appeared on “Dancing with the Stars” and written an autobiography.