On Thursday, Monica Seles announced her retirement from tennis. The 34-year-old won 53 singles titles and six doubles tournaments. She first became No.1 in the world in 1991 and held the top ranking for 178 weeks over the next two years - the youngest No. 1 ever at the time. In 1993, she was stabbed in the back during a match in Germany. She was not able to play for over two years. When she returned, she won the Canadian Open, then reached the US Open final. She won her ninth Grand Slam title at the Australian Open in 1996.