Jackie Robinson's uniform number was in the forties.
Jackie Robinson . In 1997 , MLB `` universally '' retired his uniform number , 42 , across all major league teams ; he was the first pro athlete in any sport to be so honored . MLB also adopted a new annual tradition , `` Jackie Robinson Day '' , for the first time on April 15 , 2004 , on which every player on every team wears No. 42 .