"Mannish Boy" (or "Manish Boy" as it was first labeled) is a blues standard written by Muddy Waters, Mel London, and Bo Diddley (with Waters and Diddley being credited under their birth names).

[3] Although the song contains sexual boasting, its repetition of "I'm a man, I spell M, A child, N" was understood as political.

[3] Also accompanying Muddy Waters are Jimmy Rogers on guitar, Fred Below on drums, and an unidentified female chorus.

In 1968, he recorded it for the Electric Mud album in Marshall Chess' attempt to attract the rock market.

[8] "Mannish Boy" is ranked number 425 in Rolling Stone magazine's list of the "500 Greatest Songs of All Time".