The setting where he did that was important as well: as a member of Booker T. & the M.G.’s, the house band at Memphis’s Stax Records and a rare multiracial group in the segregated South. The M.G.’s consisted of two white and two Black musicians, and their work was as American as possible, melding blues and gospel with country. It was music created when Cropper jammed in the Stax studio with the 17-year-old organist Booker T. Jones, and when he holed up in the Lorraine Motel with singer Eddie Floyd to write “Knock on Wood.”