8. Sandy Koufax:
Koufax was as dominant a major league pitcher as there ever was during his prime. He was a seven-time All-Star. Koufax won four World Series titles with the Brooklyn/Los Angeles Dodgers, winning two World Series MVP awards in those wins. He also won three Cy Youngs, led the MLB in strikeouts four times, and in wins three times. Koufax was the first MLB pitcher to throw four no-hitters as well.
But arthritis in his left elbow forced Koufax to retire at 30 years old in November 1966. Needless to say, the entirety of the baseball world was left in disarray. Koufax had just come off a season where he won an astonishing 27 games with 317 strikeouts and a peerless 1.73 earned run average (ERA).
To this day, Koufax is still ranked among the best MLB pitchers of all-time. His career obviously could have been even better had he remained healthy. But he paved the way for many more athletes to call it an early career due to injury. He may still be the most famous example of that despite the fact he retired well over 50 years ago.