John Alec Entwistle (9 October 1944 – 27 June 2002) was an English musician, songwriter, singer, film and music producer, who was best known as the bass guitarist for English rock band The Who. He was the only member of the band to have formal musical training. His aggressive lead sound influenced many rock bass players. He was inducted into the Rock and Roll Hall of Fame as a member of The Who in 1990.

John Entwistle's instrumental approach used pentatonic lead lines, and a then-unusual treble-rich sound ("full treble, full volume") created by roundwound RotoSound steel bass strings. He was nicknamed "The Ox", as well as "Thunderfingers" – because his digits became a blur across the four-string fretboard. In 2011, a Rolling Stone reader poll selected him as the greatest bassist of all time. The Biography Channel has declared that John Entwistle is considered by many to be the best bass guitarist that ever lived, and that it is often said that he did for the bass what Jimi Hendrix did for the guitar.