Philip Randolph and the Pullman Porters

In 1925, Asa Philip Randolph organized and led the Brotherhood of Sleeping Car Porters, the first predominantly African-American labor union. 

Randolph was a leader in more than one effort for social change; he helped direct the civil rights movement and the labor movement.

Perhaps Randolph's most important contribution in either of those contexts was his organizing the March on Washington movement in 1941.  That movement in turn pressured President Franklin Roosevelt to issue an executive order banning discrimination in defense industries, and, after the war, caused President Harry Truman to desegregate the United States' military.