Born Mark Norton in Hollywood, Calif., St. John was Kiss' third official guitarist, having replaced Vinnie Vincent in 1984. By this point, Kiss had done away with its trademark makeup and costumes, but the group was enjoying a career renaissance. The lone Kiss album on which St. John appeared, "Animalize," re-established the group as one of the world's top arena metal bands. The album spawned the popular MTV video, "Heaven's on Fire" (the only Kiss video to feature St. John).

St. John's flashy playing reflected the era's Van Halen-influenced rock guitarists, but it certainly helped spark the material on "Animalize," which many fans consider one of Kiss' strongest non-makeup releases. However, right around the time Kiss was to launch a worldwide tour in support of the album, St. John was diagnosed with a form of arthritis called Reiter's Syndrome, which caused his hands and arms to swell, and prevented him from playing guitar.
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His medical condition improved after leaving Kiss, and St. John launched a pop/metal outfit, White Tiger, with ex-Black Sabbath singer David Donato. Since then, St. John briefly teamed up with original Kiss drummer Peter Criss in a group that didn't release any recordings, and appeared as a guest speaker at Kiss conventions. In 2001, he released an all-instrumental album, "Magic Bullet Theory."