Doug Sahm was a singer, songwriter, and guitarist of legendary range and reputation. The first American musician to capitalize on the 1960s British invasion, Sahm vaulted to international fame leading a faux-British band called the Sir Douglas Quintet, whose hits included "She's About a Mover," "The Rains Came," and "Mendocino." He made the cover of Rolling Stone magazine in 1968 and 1971 and performed with the Grateful Dead, Dr. John, Willie...