John Glascock was a British musician. He was the bassist and occasional lead vocalist of the rock band Carmen from 1972 to 1975; and the bass guitarist for progressive rock band Jethro Tull from 1976 until his death in 1979. Glascock died at the age of 28 as a result of a congenital heart valve defect, which was worsened by an infection caused by an abscessed tooth.

Jethro Tull are a British progressive rock band formed in Blackpool, Lancashire, in 1967. Initially playing blues rock and jazz fusion, the band soon incorporated elements of English folk music, hard rock and classical music, forging a signature progressive rock sound. The group's lead vocalist, bandleader, founder, principal composer and only constant member is Ian Anderson, who also plays flute and acoustic guitar. The group has featured a succession of musicians throughout the decades, including significant contributors such as guitarists Mick Abrahams and Martin Barre ; bassists Glenn Cornick, Jeffrey Hammond, John Glascock, Dave Pegg, Jonathan Noyce and David Goodier; drummers Clive Bunker, Barrie "Barriemore" Barlow and Doane Perry; and keyboardists John Evan, Dee Palmer, Peter-John Vettese, Andrew Giddings and John O'Hara.