Bjorn Borg
Swedish tennis prodigy Bjorn Borg was just 15 when he embarked on his professional career in 1972, and he went on to win eleven Grand Slam singles titles, including a streak of three years when he won both the French Open and Wimbledon. Still in good health, he chose to end his career at age 26 apparently to escape the limelight, and has gone on to varying degrees of success since then, including a failed tennis comeback in the 90s and a lucrative sports fashion label.