Clark studied classical guitar for a year before he first heard the music of Jimmy Page and Led Zeppelin at a friend's house.

[citation needed] When Clark left school, his first employer was the engineering firm GEC Traction, where he worked as a lathe operator.

[citation needed] Before joining Def Leppard in 1978, Clark played cover songs with his band Electric Chicken in Sheffield.

According to Elliott in Behind the Music, Clark auditioned for Def Leppard by playing all of Lynyrd Skynyrd's "Free Bird" without accompaniment.

[7] Clark and Collen quickly bonded, becoming close friends and leading to the trademark dual-guitar sound of Def Leppard.

Clark was a classically trained musician who knew the rules of music and could read and write music and understood the theory and science of the art, as well as studying/being influenced by Jimmy Page and Led Zeppelin; whereas Collen, like Willis, was self-taught and developed his fast, alternate-picking technique from studying Al Di Meola and listening to jazz players.

In the liner notes of the Adrenalize deluxe edition, Joe Elliott claims that a few riffs Clark had demoed were used in a couple of places on the album.

[11] However, the deluxe rerelease of Adrenalize features a demo of the song "Tonight", which Clark performed in, having been recorded in 1988, intended to be a B-side for Hysteria.

A demo of Clark's solo was found for the song "Stand Up (Kick Love into Motion)" but was never integrated into any official material.

Shellist revealed in her autobiography, Runway Runaway, that Clark's alcoholism played a major role in their breakup.

"We'd given him six months off," recalled Joe Elliott, "told him to go and spend some time in the beautiful house he'd bought in Chelsea, eat some food he'd cooked himself, and take his clothes out of the suitcase and put them in the wardrobe.

"[16] Weeks prior to his death, Clark was found unconscious inside a bar in Minneapolis and was rushed to Hazelden Addiction Treatment Center.

According to Phil Collen, it became "almost impossible" to keep Clark sober after Dean entered his life, and almost as difficult to keep track of his whereabouts.