On April 15, 1997, the 50 anniversary of his first Major League Baseball game, the league retires Jackie Robinson’s number, 42. Robinson, whose breaking of the “color barrier” in 1947 was a major moment in the history of racial integration in the United States, is the only player in MLB history to have his number retired across all teams, a sign of the reverence with which he is regarded decades after he led the charge to integrate the major leagues.

Before 1947, Major League Baseball was, like much of America, explicitly whites-only, with Black players competing in the entirely separate Negro American League. MLB executive Branch Rickey, who was charged with exploring the possibility of integration, scouted and chose Robinson to break the league’s color barrier both because of his talent and because he believed Robinson would be able to endure the racist abuse that would undoubtedly be hurled his way. Robinson did indeed face racist taunts from fans, abuse and rough play from his opponents, and even racist remarks from his own teammates during the 1947 season.

Nonetheless, he proved that African American players could not only compete but could thrive in MLB, leading the league in stolen bases and winning National League Rookie of the Year. By the time of his retirement in 1956, Robinson had won the Most Valuable Player award, been named to six All-Star teams, and won the 1955 World Series, a list of accomplishments that would have made any player a likely candidate for the Hall of Fame. He was elected to the Hall of Fame as soon as he was eligible in 1962, and the Dodgers retired his number shortly before his death in 1972.

In a 1997 ceremony attended by Robinson’s widow and President Bill Clinton, MLB Commissioner Bud Selig said, “Number 42 belongs to Jackie Robinson for the ages.” Certain players who wore the number at the time were permitted to do so for the remainder of their career—thus the New York Yankees’ Hall of Fame closer Mariano Rivera was the last-ever player to wear the number, playing his final game in 2013. Wayne Gretzky, whose domination of the National Hockey League earned him the nickname The Great One, is the only other player to have his number retired across every team in a major American sports league. Today, Robinson and the number he wore remain synonymous with the struggle to end segregation in American sports.