He is best known to the general public for his role as Floki in the television series Vikings.
He played his first film role when he was nine years old in Täcknamn Coq Rouge (Eric Hamilton). Gustaf's father played a major role in this film. From 1999 to 2003 he studied at the Stockholm Academy of Theater Arts (Swedish: Teaterhögskolan). Since 2003, he has worked in the theater, playing leading roles in many productions (The Merchant of Venice). Continuing to play in the theater, he took part in a number of television productions, and also acted in films. The most famous role of Gustaf in 2002 in the film "Invisible" (Swedish: Den osynlige). In 2003, he starred in the film Evil, which was nominated for an Oscar. In 2007, he was awarded the Golden Bug Award (Swedish analogue of the Oscar Award) for the film "Children of the Outskirts", and was also nominated for it twice: in 2004 for participating in the film "Evil", and in 2009 for the film " Patrick 1.5".

Filmography:

Year			Film
1989			Täcknamn Coq Rouge
1989			Prima ballerina
1994			Euroboy
1994			Min vän Percys magiska gymnastikskor
1995			Sommaren
1996			Skuggornas hus
2002			Den osynlige
2002			Gåvan
2002			Cleo
2002			Kontrakt
2003			Ondskan
2003			Detaljer
2003			Swedenhielms
2004			Ikke naken
2004			Babylonsjukan
2006			Förkväll
2006			Förortsungar
2006			Snapphanar
2007			Arn: Tempelriddaren
2007			Pyramiden
2008			Mellan 11 och 12
2008			Iskariot
2008			Arn: Riket vid vägens slut
2008			Patrik 1,5
2009			May Fly
2010			Arn
2010			Puss
2010			The Way Back
2011			Happy End
2011			Bibliotekstjuven
2012			Kon-Tiki
2013			The Big Leap
2013			Autumn Blood
2013			VI
2013—2020			Vikings
2013			The Galapagos Affair: Satan Came to Eden
2014			Ettor nollor
2014			Tjuvarnas jul – Trollkarlens dotter
2015			Vikings: Athelstan's Journal
2017			Darling
2018			Westworld
2018			Little Match Girl
2019			438 dagar
2020			Cursed
2021			Utvandrarna
2022			Blood
2022			Soul of a Man
2022			Utvandrarna
2022			What Remains
2023			Air
2023			Oppenheimer
TBA			Ondskan