On Wednesday night, Serena Williams won her second round match against no. 2 ranked Anett Kontaveit, to advance in what could be the last pro tournament of her career. Earlier this month, Williams hinted that it might be time to say farewell to her illustrious tennis career. For two decades, the star has dominated the sport, winning 23 grand slam singles titles, 14 women's doubles and two mixed doubles slams. Cecil Harris, sports journalist and the author of 2020's Different Strokes: Serena, Venus and the Unfinished Black Tennis Revolution and the host of podcast All-American: Venus and Serena, explains why many say Williams is “the greatest of all time” in the tennis world.