John Alec Entwistle (9 October 1944 - 27 June 2002) was an English bass guitarist, songwriter, singer, and horn (Horn (instrument)) player, who was best known as the bass guitarist for the rock band The Who. His aggressive lead sound influenced many rock (Rock music) bass players. He has been described as "the greatest bassist in the history of rock" by Greenwich Time (Greenwich Time_(newspaper)) and The Ledger.

Entwistles lead instrument approach used pentatonic (Pentatonic scale) lead lines, and a then-unusual trebly sound created by roundwound (Strings (music)#Roundwound) RotoSound steel bass strings. He had a collection of over 200 instruments by the time of his death, reflecting the different brands he used over his career: Fender (Fender Musical Instruments Corporation) and Rickenbacker basses in the 1960s, Gibson (Gibson Guitar Corporation) and Alembic (Alembic Inc)s basses in the 1970s, Warwick (Warwick (bass guitar)) in the 1980s, and Status all-graphite (Carbon fiber) basses in the 1990s.