#4 Ai Sugiyama
No Japanese tennis player barring Ai Sugiyama has reached the summit of the tennis rankings, be it at the ATP level or WTA level.
Sugiyama was the No. 1 ranked doubles player in October 2000. She also reached a career-high ranking of World No. 8 in singles.
In her 17-year WTA career, Sugiyama won 6 WTA Singles titles and an impressive 28 WTA Doubles titles. At the doubles level she made the finals of all 4 Grand Slams, winning all but the Australian Open where she finished runner-up in 2009 (the year she retired).
Sugiyama also won the 1999 US Open mixed doubles title partnering India's Mahesh Bhupathi.
Sugiyama enjoyed considerable success in singles too. Her best Grand Slam results were quarterfinal appearances at the Australian Open in 2000 and the Wimbledon Championships in 2004.
Sugiyama held the all-time record, for both male and female players, for her 62 consecutive Grand Slam main draw appearances, until she was surpassed by Roger Federer at the 2015 Wimbledon.