UFO practically invented pop-metal, paving the way for future stars like Def Leppard. They formed in 1969 as early purveyors of hard rock and prog, but their first few albums went largely ignored. The addition of ex-Scorpions guitarist Michael Schenker changed all that, and songs from '74's Phenomenon became radio staples. A string of classic albums ensued, including the monster Light's Out and the killer live set Strangers In the Night. Schenker quit in '78, and the band's fortunes waned in the '80s, but they continue to record and do big tour business.