The son of a Swedish father and an Irish mother, Castel was born Ulv Quarzell in Bogotá, Colombia, where his father was working as a diplomat. He and his twin brother grew up in Cartagena.[1]
When Castel was 6, his parents separated. He followed his mother to Europe and went to school in London, very briefly at Dartington Hall School with his sister Solveig, then in Stockholm. He subsequently went to live in Rome where his mother was working in the local film industry. A communist, Castel's mother also introduced her son to politics.[1]
While living in Italy, Castel became involved in a maoist organization, the Union of Italian Communists (Marxist–Leninist). As Italy was going through the Years of Lead period, he was eventually considered an undesirable alien. In 1972, he was deported to Sweden where he no longer had any acquaintances. For a time, he had to rely on subsidies sent to him from Italy by his organization. However, he quickly bounced back and appeared, mostly as a character actor, in various European films, directed by filmmakers such as Wim Wenders and Claude Chabrol.[1]
Castel settled in France in the early 1990s.[1] Though the quality of the films he acted in were quite disparate, ranging from arthouse films to cheap exploitation, Castel had a preference for roles that reflected his extreme leftist beliefs. He portrayed left-wing terrorists in Nada (1974), The Cassandra Crossing (1976), Could It Happen Here? (1977) and Year of the Gun (1991).
A polyglot, Castel speaks a number of languages but jokes that he has no real natural mother tongue and speaks every language with an accent, except for Swedish which he no longer has opportunities to use.[1]
