"You know,” Def Leppard guitarist Phil Collen says, “we weren’t doing what we were doing to be different. We were a bit different.” What they did was create one of the more forward-thinking, over-the-top and ultimately successful albums in rock history: Hysteria. Released 25 years ago this summer, the record spawned an astonishing seven hit singles, including “Animal,” “Love Bites” and the monster smash “Pour Some Sugar on Me.” It also hit Number One on the U.S. album chart—three times, no less—and went on to sell more than 20 million copies worldwide.