Sports: Baseball & Football
Career Years: Football (1915-1917, 1919-1926, 1928) Baseball (1913-1915, 1917-1919)

Simply put, Jim Thorpe is the greatest athlete of all time that you may never have heard of. Dude received gold medals at the 1912 Olympics for decathlon and pentathlon. Then he made his MLB debut as an outfielder with the New York Giants in 1913. Then in 1915, he joined the Canton Bulldogs in the American Professional Football Association which would later become the NFL. He spent seven years in MLB and 13 seasons in the NFL. Without a doubt the best multi-sport athlete of all time.