Real name: Karl Johan Schuster

Karl Johan Schuster (Born February 1, 1985), known as Shellback, is an artist from Karlshamn, Sweden.

Before he became part of Max Martin's Maratone production studio in 2007 he was a a drummer in local indie rock bands in Karlshamn. He also was a member of hardcore / metal band Blinded Colony.

He co-wrote Pink's 2008 single "So What" , and Britney Spears's 2008 single "If U Seek Amy".