Most people who pay attention to such things credit Ken Griffey Jr. with starting the annual tradition of all MLB players wearing #42 on April 15, Jackie Robinson Day. In 2007 Griffey asked Commissioner Bud Selig for special permission to wear the number on the 15th. Selig confirmed with Rachel Robinson that it was okay, and a tradition was born. But prior to that 2007 request, Griffey once wore # 42 as a Mariner. In 1997, during the league's 50th Braking Barriers celebration Griffey flipped his #24 to #42. He was the only player to do so on that date.