The main players in the integration of baseball were the first three integrated players Jackie Robinson, Larry Doby, and Hank Thompson.
Jackie Robision was the first African American to play in the MLB. He signed with the Brooklyn Dodgers in 1947.
Larry Doby was the second player to be integrated into baseball. He came from the Newark Eagles as an infield star and joined the Cleveland Indians in 1947.
Also, Hank Thompson, the third integrated player, was a third baseman for the Negro League Monarchs. He made his Mlb debut with the St. Louis Browns on July 17, 1947.
They were all key factors in the integration of baseball because if one of them messed up, the league could kick out all blacks in the MLB.