Joseph Elliott, a lead vocalist in Def Leppard, made a poster of with a jungle cat with a hearing horn in it's ear. He called it the Deaf Leppard. The band liked it so they shortened it to Def Leppard and used it as the bands name.
Def Leppard started out as Atomic Mass. A band that included, Rick Savage and Pete Willis in 1977. As fate would have it, Joe Elliott had missed his bus and ran into Pete Willis and was invited to audition for the band.
Rick Allen has been the drummer for Def Leppard all their career. Actually, Tony Kenning was the original drummer for Def Leppard. Then Frank Noon was the drummer for just a few days. Rick Allen then became the permanent drummer for the band.
In America and Canada, Def Leppard have sold more records; but everywhere else in the world, Iron Maiden have sold more records. So generally, Iron Maiden have sold more records around the world than Def Leppard.