was recruited into the band to replace him. Clark and Collen quickly bonded, becoming close friends and leading to the trademark dual-guitar sound of Def Leppard. He and Collen became known as the "Terror Twins" in recognition of their close friendship and alcohol-fueled antics offstage. Part of their success as a duo was attributed to their ability to swap between rhythm and lead guitar, with both playing lead or both doing rhythm within the same song. The fact that they came from entirely different musical backgrounds also contributed to their unique guitar partnership. 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. Clark once said, "I do read and write and I know the rules of music which is great in a two-guitar band because we're so different in our approach to playing. Phil will play something if it sounds right, whereas I look at things and say: 'it's wrong to play that note; it's not musically correct'." Clark primarily played Gibson Guitars during his career and signed an endorsement with Gibson in 1987. Gibson made some custom-specification guitars for Clark. He was occasionally seen playing other guitars, including a Fender Stratocaster for the song and video "Love Bites". Clark would also use Fenders in the studio occasionally, due to their unique sound. Although his name appears on many songwriting credits for Def Leppard's 1992 album, Adrenalize, he did not contribute much to the recording of the album. 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. His only other contribution was an occasional approval of what the rest of the band was working on, referring to it as "cool". The song "White Lightning" described the effects of Clark's alcohol and drug addictions. 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. Clark was involved in the recording of the demo for the band's 1995 single "When Love & Hate