Serena Williams is considered one of the greatest tennis players of all time, having won 23 Grand Slam singles titles during the Open Era, the most for any man or woman. She has also won 14 Grand Slam doubles titles with her sister, Venus, and four Olympic gold medals. Williams also tied the WTA record for most consecutive weeks at No. 1 with 186. The athlete is at the center of a new HBO documentary series, Being Serena, which premieres May 2.