Martina Hingis is retiring after the Singapore finals
Her illustrious career includes dominating the singles game as a 16 year old in the late 90s, retiring due to injuries, a short-lived comeback in the mid 2000s that ended with a controversial two year ban for a positive cocaine drug test, and a third doubles comeback in 2013. She has a total of 5 singles Slams, 13 womens doubles Slams, 7 mixed doubles Slams, countless WTA titles and a bunch of youngest ever records unlikely to be broken in our lifetime. She is retiring as the worlds number 1 ranked doubles player, and is currently on a huge win streak (20 matches?) with her partner Latisha Chan, with only one or two matches left to play in her career, at the WTA Finals.
Martina was my favorite pro player as a kid in the 90s I used to live for her epic matches against the Williams sisters. To watch her win Slams decades later has been awesome! And of course she does it with such flair, almost never being able to match her opponents power, but still beating them all anyway

I hope she makes a 4th comeback in her 40s, after she has kids or whatever, and sets a bunch of oldest ever records. Why not?!