Karl Johan Schuster (; born 1 February 1985), known professionally as
Shellback, is a Swedish songwriter, record producer and musician. 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 regularly collaborates with songwriter
Max Martin, and together they have produced, written and/or co-written songs for
P!nk ("
So What", "
Raise Your Glass", "
Fuckin' Perfect"),
Taylor Swift ("
We Are Never Ever Getting Back Together", "
I Knew You Were Trouble", "
22", "
Shake It Off", "
Blank Space", "
Style", "
Bad Blood", "
Wildest Dreams"),
Adam Lambert ("
Whataya Want from Me", "
If I Had You"),
Britney Spears ("
If U Seek Amy", "
3", "
I Wanna Go"),
Usher ("
DJ Got Us Fallin' in Love", "
Scream"),
Avril Lavigne ("
What the Hell", "
Wish You Were Here"),
Ariana Grande ("
Problem"),
Adele ("Send My Love (To Your New Lover)"), and
Maroon 5 ("
One More Night"). Shellback has collaborated with fellow producer
Benny Blanco for "
Payphone" and "
Moves like Jagger" by
Maroon 5 and "
She Doesn't Mind" by
Sean Paul. He has also produced songs by himself, including "
Want U Back" by
Cher Lloyd and "
Animals" by Maroon 5.