Bjorn Borg: The suave Swede was a dominant force in the men’s game for much of the late 1970s and early ’80s. 
But he abruptly announced his retirement in January 1983, aged 26.

Martina Hingis: In 1997, Hingis became the youngest Grand Slam singles winner, winning the Aus Open aged 16 years and three months. She struggled with ankle injuries and at 22 retired in 2003.