"Mannish Boy", or "Manish Boy" as it was first named, is a blues standard first recorded by Muddy Waters in 1955. The song was a hit and reached #5 during a stay of six weeks in the Billboard R&B chart. It is a arrangement of (and an "answer song" to) Bo Diddley's "I'm a Man" (which in turn was inspired by Waters' and Willie Dixon's "Hoochie Coochie Man"). "Mannish Boy" features a repeating stop-time figure on one chord through out the song and is credited to Waters, Mel London, and Bo Diddley. Backing Muddy Waters (vocal and guitar) are: Otis Spann (piano), Jimmy Rogers (guitar), Willie Dixon (bass), Francis Clay (drums), and either Junior Wells or Little Walter (harmonica).
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http://en.wikipedia.org/wiki/Mannish_Boy