John William "Billy" Mackel (December 28, 1912 – May 5, 1986) was a distinguished American jazz guitarist born in Baltimore, Maryland. Initially, Mackel played the banjo before transitioning to the guitar in the 1930s, a common shift among banjoists of that era. He led his own band in the early 1940s before joining the renowned Lionel Hampton's big band in 1944. Mackel remained with Hampton for over three decades, contributing significantly as a rhythm guitarist. His tenure with Hampton included extensive touring and recording, during which he displayed a freewheeling style and a strong foundation in blues and R&B.

In addition to his work with Hampton, Mackel recorded with notable artists such as Milt Buckner, Arnett Cobb, and Herbie Fields in the 1940s, and collaborated with Billy Williams in the 1960s. Mackel was known for his left-handed guitar playing and occasionally arranged pieces for Hampton's band, demonstrating a keen ear for bop nuances. His discography includes recordings like "At Last" with Eddie Chamblee and others, released in 1977. Mackel passed away in Baltimore at the age of 73, leaving behind a legacy as a prominent figure in the jazz guitar scene.