Johnny Mercer's main claim to immortality is his incredible songwriting output, penning the lyrics or music and lyrics to roughly 1,500 songs. Marked by a sophisticated, occasionally whimsical mastery of language and rhymes, many of Mercer's songs have become standards regularly covered by jazz artists. Yet he was also a successful singer, with a relaxed, Southern-accented, jazzy, rhythmically agile delivery that resulted in several major hits in the 1940s. At first, he was torn between acting and songwriting, but having failed to land a part in Garrick Gaities in 1930, he end...