Frederic Wilhelm C.J. Sjöström (born 8 January 1987) is an English actor and model, best known for playing Cormac McLaggen in the Harry Potter film series and Luke in the 2012 musical comedy film Pitch Perfect. He starred as Adam Cromwell on the dramedy series UnREAL, which premiered on Lifetime in June 2015. He starred as Brit Vayner in the 2016 Michael Bay war film, 13 Hours: The Secret Soldiers of Benghazi. And in April 2016, he will play Dickon Tarly during the sixth season of the HBO fantasy drama series Game of Thrones.
Stroma was born in London, England, to father Stefan Sjöström, a Swedish-born computer industry executive, and a German mother, and grew up in Ascot, England in the East Berkshire county, about 25 miles west of London. He was educated at the public boys'-only boarding school Radley College in Oxfordshire, graduating in 2005. He has an older sister and a younger brother, Philipp Sjöström.
When he was 16, Stroma was accepted to the National Youth Theatre of Great Britain. He had roles on various British TV shows, including Casualty and BBC's detective show, Mayo (aka The Gil Mayo Mysteries). While studying neuroscience at University College London, Stroma continued to work as an actor and model. He ended up taking a year off from university to play the role of Cormac McLaggen in Harry Potter and the Half-Blood Prince. After filming was over, Stroma completed his degree at University College London. In 2009, he attained a 2:1 BSc (an upper-second-class degree) in Neuroscience.