Emma Raducanu rose to the top of tennis quicker than anyone expected. But staying there will require management - both on and off the court.
Daniil Medvedev, who won the US Open in 2021, is the defending ATP Finals champion having won the title in 2020.
The 20-year-old Jannik Sinner is in with an outside chance of making the ATP Finals. But his 2021 season has been excellent regardless.
The Bryan brothers changed the entire landscape of doubles in Tennis by winning 15 Grand Slams and 1000 matches.
David Nalbandian became the first player to win the year-ending ATP Final title without winning a Grand Slam title.
Diede de Groot and Dylan Alcott achieved the Golden Grand Slam in the same year, redefining dominance in the spor of Tennis.
Steffi Graf became the first to pull off a calendar Golden Slam in 1988. Till date, she remains the only able-bodied tennis player to do so.
Serena Williams has remained a force in the sport of tennis since she made her debut and, even now, remains the woman to beat on the WTA tour.
Juan Martin del Potro defeated Rafael Nadal and Roger Federer in the same Grand Slam to win the US Open in 2009.
Rod Laver achieved the Calendar Grand Slam in both the Amateur and Open Era and this achievement might never be matched.