Jackie Robinson wore jersey number 42.
Robinson wore number 42 during his historic Brooklyn Dodgers career, including his 1947 major league debut. The number became inseparable from his role in breaking Major League Baseball’s modern color line: on April 15, 1947, he started at first base for Brooklyn at Ebbets Field and became the first Black player in MLB in the modern era.
The Dodgers retired Robinson’s number in 1972. Major League Baseball retired number 42 across every team on April 15, 1997, the 50th anniversary of his debut. A grandfather clause allowed players already wearing it to continue temporarily; Mariano Rivera was the last player to wear 42 regularly, retiring after the 2013 season.
Today, players and on-field personnel wear 42 on Jackie Robinson Day, held annually on April 15. That special observance does not make 42 available as a normal roster number. The number is therefore both a jersey identifier from Robinson’s playing days and one of the most prominent retired numbers in professional sports.