Alexander Stephen Hassell (born 7 September 1980) is an English actor. He is co-founder of The Factory Theatre Company. Hassell was born in Southend, England, the youngest of four, to a vicar. He trained at the Central School of Speech and Drama after completing GCSE and A-Level courses at Moulsham High School, in Chelmsford, Essex.

He has appeared in a number of stage roles, most recently as Hal in Henry IV Parts I and II, and Henry in Henry V, for the Royal Shakespeare Company. His first Hollywood role was in George Clooney's Suburbicon (2017), and later that year he appeared in his first major television role in the BBC adaptation of Jessie Burton's The Miniaturist, which first aired on Boxing Day. He also appeared as Translucent in the first season of The Boys (2019) on Amazon Prime Video, and played Vicious in Netflix's Cowboy Bebop in 2021.