Who is "Shellback"?

Karl Johan Schuster (born 1 February 1985), known professionally as Shellback, is a Swedish songwriter, record producer, and multi-instrumentalist. Shellback was listed as the No. 1 producer of 2012 on Billboard magazine's year end chart, and he also topped the list of their "Top 10 Songwriters Airplay Chart" the same year; he has won four Grammy Awards.

He regularly collaborates with songwriter Max Martin, and together they have produced, written, or co-written songs for P!nk, Taylor Swift, Adam Lambert, Britney Spears, Usher, Avril Lavigne, Ariana Grande, Adele, and Maroon 5. Shellback has also collaborated with fellow producer Benny Blanco and has produced songs by himself, including "Want U Back" by Cher Lloyd and "Animals" by Maroon 5.

Karl Johan Schuster was born and raised in Karlshamn, Sweden. He started as a drummer in local indie rock bands in Karlshamn, as well as recording all instruments on the 2003 Meriah demo ...Turn Him Your Other Cheek (a strictly black metal recording), before joining the hardcore-metal scene as a vocalist in 2004 for Blinded Colony, with whom he recorded 2005's Promo Demo and 2006's Bedtime Prayers, drawing comparisons to fellow Swedish melodic death metal band In Flames, before leaving in 2007. In 2005 he also performed as a guest musician on the Faith album Sorg.