John Alec Entwistle (9 October 1944 – 27 June 2002) was an English bass guitarist, singer, songwriter, and film and music producer. In a music career that spanned more than 40 years, Entwistle was best known as the original bass guitarist for the English rock band the Who. He was the only member of the band to have formal musical training. He was inducted into the Rock and Roll Hall of Fame as a member of the Who in 1990.

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" and "Thunderfingers". In 2011, he was voted as the greatest bass guitarist of all time in a Rolling Stone magazine readers' poll, and in its special "100 Greatest Bass Players" issue in 2017, Bass Player magazine named Entwistle at number seven.