John Glascock (2 May 1951 – 17 November 1979) was a British bass guitarist and singer. Glascock was best known for being the bassist and occasional lead vocalist of the rock band Carmen from 1972 to 1975 as well as 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.

In a September 1978 Guitar Player interview, Ritchie Blackmore had said "... John Glascock is a brilliant bass player, the best in the business in rock.

The first band John Glascock played with was The Juniors (1962–1964). He then played with The Gods (early 1965 – June 1967, September 1967 – February 1969), where, together with future Uriah Heep members Ken Hensley and Lee Kerslake, he recorded the album Genesis. After briefly playing with Head Machine (1970), he joined Toe Fat (June 1969 – December 1970), again with Hensley and Kerslake. With Chicken Shack (January 1971 – March 1972) Glascock recorded only the album Imagination Lady. His brother Brian Glascock also played drums in Toe Fat.

In 1973 he joined Carmen. With them, John Glascock played bass guitar, sang backup vocals, occasionally played synthesizers, and even sang lead vocals on a few songs. These songs include "The City", "Dancing On a Cold Wind" (sharing lead vocals with David Allen), and "The Horseman" (sharing vocal duties with all of Carmen), all from the album Dancing on a Cold Wind (1974). He also sang on the track "High Time" from the album The Gypsies (1975).

Glascock's basslines in Carmen were often technical and unusual. They were key to Carmen's unique sound. Unlike his work in Jethro Tull, Glascock utilized effects in his sound while with Carmen, like a fuzz pedal in the song "Viva Mi Sevilla". Glascock had only one writing credit on the first album recorded by Carmen, Fandangos in Space (1973), the short track "Retirando". He shared this writing credit with the rest of the band.

His writing expanded greatly by the time of the second album, Dancing on a Cold Wind (1974). On this album he had a writing credit for three songs, "Viva Mi Sevilla" (which he shares with the rest of the band), "Purple Flowers" (which he shares with Roberto Amaral), and "Remembrances" (which he shares with the rest of the band).

His writing had reached a climax by the time of Carmen's third and final album, The Gypsies (1975). On this album he wrote "High Time" by himself, and sang lead vocals on it. He and the rest of the band also share a writing credit on the instrumental track "Margarita".

Glascock then joined Jethro Tull in 1976, after having met Ian Anderson when Carmen opened several dates for Jethro Tull on their War Child tour. Martin Barre said in the "Classic Artists Series" documentary, that Glascock's love for the band was unique: being a fan of Jethro Tull and playing in the band. He played on the Jethro Tull albums Too Old to Rock 'n' Roll: Too Young to Die! (1976), Songs from the Wood (1977), Heavy Horses (1978), Bursting Out (1978), and on three tracks on Stormwatch (1979). In Jethro Tull he received no writing credits but sang backing vocals, and became the first harmony vocalist Jethro Tull had.[2]

Glascock replaced the longtime friend of Ian Anderson, Jeffrey Hammond. He also played electric guitar on-stage when Anderson's arrangement required it, as for instance in performances of "Skating Away on the Thin Ice of the New Day" from the Bursting Out live album, when the rest of the band was playing xylophone, glockenspiel and percussion.

Glascock's health problems became apparent when he was unable to complete the U.S. leg of the Heavy Horses tour, missing a transatlantic simulcast from Madison Square Garden. He played his last concert on 1 May 1979, in San Antonio, Texas, three years to the day of his first concert with Jethro Tull.[3] Despite the diagnosis of heart valve damage caused by an infection, he continued his previous lifestyle, which involved heavy drinking, marijuana usage, and wild parties. His health continued to deteriorate. Ian Anderson gave him several warnings before finally laying him off with pay during the production of Stormwatch (1979), completing most of the bass guitar parts himself. During the subsequent promotional tour with replacement bass player Dave Pegg, Anderson learned of Glascock's death and had to break the news to the rest of the band. Glascock's close friend, drummer Barriemore Barlow, was devastated and left the band at the end of the tour.[4]

The resulting dislocation, Ian Anderson's own artistic vision, and a decision from the label, prompted a complete overhaul of the lineup, leaving only Anderson and Martin Barre as full members, though Glascock's touring replacement on bass (Dave Pegg) was retained for the band's follow-up album in 1980 and would remain with the group till 1995.

John Glascock had a relationship with bandmate Angela Allen while in Carmen and sometime after. Glascock was well liked by his Jethro Tull bandmates, and had a particularly close relationship with Barriemore Barlow. Barlow paid for Glascock's funeral, as Glascock died with almost no money. He had made what Barlow considered a "terrible contract" with Ian Anderson – this was one of the reasons for Barlow's eventual departure.

During Carmen there are photographs and video of John Glascock with a Rickenbacker 4001 as well as a Gibson EB3. He also used distortion and wah pedals on the Dancing on a Cold Wind album. In Jethro Tull, John Glascock generally used Fender Precision basses and Music Man StingRay basses. When he needed to use an acoustic bass, he would use a Yamaha Acoustic. For amplification, he used Martin bass bins, Crown amps, Martin pre-amps, and Acoustic pre-amps.