Serena Jameka Williams (born September 26, 1981) is an American professional tennis player. The Women's Tennis Association (WTA) ranked her world No. 1 in singles on eight separate occasions between 2002 and 2017. She reached the No. 1 ranking for the first time on July 8, 2002. On her sixth occasion, she held the ranking for 186 consecutive weeks, tying the record set by Steffi Graf. In total, she has been No. 1 for 319 weeks, which ranks third in the "Open Era" among female players behind Graf and Martina Navratilova.
Williams holds the most Grand Slam titles in singles, doubles, and mixed doubles combined among active players. Her 39 major titles puts her joint-third on the all-time list and second in the Open Era: 23 in singles, 14 in women's doubles, and two in mixed doubles. She is the most recent female player to have held all four Grand Slam singles titles simultaneously (2002–03 and 2014–15) and the third player to achieve this twice, after Rod Laver and Graf. She is also the most recent player to have won a Grand Slam title on each surface (hard, clay and grass) in one calendar year. She is also, together with her sister Venus, the most recent player to have held all four Grand Slam women's doubles titles simultaneously (2009–10).
Her total of 23 Grand Slam singles titles marks the record for the most Grand Slam tournament wins in the Open Era, and is second on the all-time list behind Margaret Court (24). She has won an all-time record of 13 Grand Slam singles titles on hard court. Williams holds the Open Era record for most titles won at the Australian Open (7) and shares the Open Era record for most titles won at the US Open with Chris Evert (6). She also holds the all-time record for the most women's singles matches won at majors with 335 matches.