I'd say Gordie Howe or Jim Thorpe. Hard to compare the two different sports they "majored" in, but Howe played hockey at a competent level in the NHL until his 50s, even played in the all-star game in his final season, I believe. He used to work out with the Detroit Tigers in his spare time. Rick Reilly of Sports Illustrated says he was the most versatile athlete ever because he was his own goon.
To play as long as he did in an era when the NHL was much bloodier than it is now, and without helmets or even likely much proper medical care compared to today, to bounce back from a life-threatening head injury early in his career and still excel for so many years is a true sign of grit and talent.
