Go to any concert, any music festival, and there will be scores of opening acts. They serve to get the crowd warmed up, get the crowd ready to rock with the headliners at the end of the night. This same thing used to happen at political events: Sometimes other political figures aside from the "headliner" would give speeches of their own for the cause and often musicians with sympathizing views would perform as well. This same thing happened at the conclusion of the March on Washington for Jobs and Freedom, which culminated in Martin Luther King's famous "I Have A Dream" Speech. There was no doubt that King was the "headliner," but he had a heck of an opening set from a series of iconic musicians. Here's a list of the esteemed performers who played at the same podium as Dr. King that did.
Mahalia Jackson was known as the "queen of Gospel" for her career in music and she was also heavily involved in the Civil Rights movement. If anyone deserved to be a performer prior to King's appearance at the Lincoln Monument, it deserved to be her. She gave an incredible performance of the Gospel standard "How I Got Over," a tale of how the protagonist got into heaven. There was a less than subtle connection between the spiritual world and the political world in many Gospel songs, translating the struggles of blacks in American to the struggles of the Jews in the desert during the Old Testament. Her role backing King was more important to music however: She stood behind the Civil Rights leader during his speech, and as he broke away from his prepared remarks and gained emotional momentum she shouted "tell them about the dream, Martin!" And he did. The rest is history.
Bob Dylan and Joan Baez
This was about as big a "supergroup" as could exist at the time (outside of whatever Miles Davis put together during that era). Dylan was in his prime as a protester (under the alias of "Hobo Bob" and his later Joan Baez is also one of the biggest names in American old music history. Both had more experience in pushing for the rights of the working class but those messages didn't run counter to the primary purpose of the March on Washington. The pair performed "When The Ship Comes In," a sensible choice, but the more interesting song was "Only A Pawn in Their Game." That track discussed how Byron de la Beckwith, a Southerner booked in the race-driven murder of a black man, wasn't actually to blame but rather was just a tool in the racist motive of the government. That wasn't exactly in line with what Civil Rights activists were arguing at the time.
Marian Anderson is perhaps the most underrated of the performers present for the March on Washington. She, like Jackson, was involved in the Civil Rights movement for far longer than that day. Although she performed another Gospel classic, "He's Got The Whole World In His Hands"—which has much less to do with the Civil Rights movement than the song Jackson would perform—her most relevant moment on the steps of the Lincoln Memorial had come nearly 25 years earlier. She had been booked to sing for an event hosted by the Daughters of The American Revolution until that organization found out she was black. Eleanor Roosevelt and other members of the group threatened to cancel their memberships if Anderson wasn't allowed to perform. Needless to say, she performed. Her rendition of "My Country 'Tis of Thee" was a glorious moment for black performers everywhere.
Peter, Paul and Mary
Peter, Paul and Mary were one of the other hot acts in the folk scene at the time, and it should be noted that no genre showed as much support for the Civil Rights movement as folk, from performer both black and white. It's humorous to note that one of the songs the trio opted to perform was "Blowin' In The Wind," a now classic by Bob Dylan that at the time had only just come out. It's possible that many in the audience didn't even realize they were covering an act who was there performing as well. The trio also performed "If I Had A Hammer," a worker's song that had been made popular decades earlier by The Almanac Singers.