Eric Byrnes
Hank aAron
Roberto Alomar
Dizzy Dean
Jackie Robinson wore #21 for the Brooklyn Dodgers for ten seasons (1947-56).
Babe Ruth
Dan Durante
Eric Byrnes
Lee may micky tettlton
Don't know of any famous, or otherwise, baseball player that wore a "?" Better rephrase your question.
Casey Stengel and Bill Lee
Babe Ruth
Hank aAron
Roberto Alomar
Dizzy Dean
Lou Gehrig with the New York Yankees
John Elway.