Roberto Clemente
Roberto Clemente was a well-known Puerto Rican baseball player who was drafted and played for the Pittsburgh Pirates throughout the course of his 17-year-long career. He had discreetly considered joining the military during those years as an athlete and finally decided to go for it while his teammates were preparing for the rough upcoming winter in his native country. He enlisted in the US Marine Corps reserves without anyone becoming the wiser in the 1950s.
He understood that marine training had toned his physique, and his baseball career had benefited from it immensely. The 15-time All-Star did, however, leave the military in 1964 to prepare for the World Series.