Following his 1987 exit from the German power metal band Accept, vocalist Udo Dirkschneider formed U.D.O. with guitarists Peter Szigeti and Mathias Dieth, bassist Frank Rittel, and drummer Tomas Franke. The group's debut album, Animal House, was in fact written by Dirkschneider's former bandmates in Accept, and by the time of the 1988 follow-up Mean Machine, Szigeti, Rittel, and Franke had all been dismissed, replaced by guitarist Andy Susemihl, bassist Thomas Smuszynski, and drummer Stefan Schwarzmann. Susemihl himself was out of U.D.O. for 1990's Faceless World, replaced by guitarist Wolla Böhm; the same roster recorded 1991's Time Bomb, although the band split in the wake of a subsequent tour, with Dirkschneider rejoining Accept from 1992 to 1996. He re-formed U.D.O. with Dieth, Schwarzmann, guitarist Stefan Kaufmann, and bassist Michael Voss to contribute a track to the Judas Priest tribute album Legends of Metal; only Schwarzmann and Kaufmann remained on board for 1997's full-length Solid, which featured new guitarist Jürgen Graf-Biardi and bassist Fitty Wienhold. No Limits followed a year later, and in 1999 U.D.O. resurfaced with Holy. 2002's Man and Machine featured the hit "Dancing with an Angel," a duet with Warlock vocalist Doro Pesch, and was followed by the studio albums Thunderball (2004), Mission No. X (2005), Mastercutor (2007), Dominator (2009), and Rev-Raptor (2011). The following year saw the departure of guitarist Stefan Kaufmann, who had to leave the fold for health reasons. He was replaced by Andrey Smirnov, who made his first studio appearance with the group on 2013's Steelhammer. Decadent, the band's 15th long player, arrived in a timely fashion in early 2015. ~ Jason Ankeny