We conclude our Summer of Soul series with Mavis Staples and Gladys Knight, two performers featured in Questlove's documentary about the 1969 Harlem Cultural Festival. As a teenager, Mavis Staples performed with her family in the Staple Singers, led by her father, "Pops" Staples. By the late '50s, the Staple Singers was one of the most popular gospel groups in the country. In the early '70s, they crossed over to the top of the pop charts.Gladys Knight's Motown hits with the Pips included "I heard it Through the Grapevine," "Neither One of Us," and "The End of Our Road." She had one of her biggest hits after leaving Motown: "Midnight Train to Georgia."