Since Charlie Chaplin and Mary Pickford campaigned for the sale of war bonds until the present day, when Richard Gere, Brad Pitt and George Clooney are riding their own political hobby horses, film stars have used their fame to crusade for some cause or another. The actor Ron Silver, who has died of oesophageal cancer aged 62, was more politically active than most, often becoming associated more with Capitol Hill than Beverly Hills. "I'm an actor by calling but an activist by inclination," Silver once explained. This side of Silver resulted in his alienating many of his colleagues in the film industry, especially when his views shifted drastically from left to right.
Silver was born in New York, the son of Jewish immigrants, in the Lower East Side of Manhattan. His father was an executive in the menswear business, his mother a supply teacher. Working his way through the state school system, Silver finally graduated with a master's degree in Asian studies at St John's University in New York and the College of Chinese Culture in Taiwan, with the intention of becoming a China expert for the CIA.
Back home, deciding that he had all the attributes to become an actor - dark good looks, piercing eyes, a sonorous speaking voice and few inhibitions - he trained at the Herbert Berghof Studios and the Actors Studio. He began his acting career in the early 1970s on stage in the off-Broadway musical revue El Grande de Coca-Cola (1973). There followed several years in television series, notably in Rhoda, as the eponymous bachelor girl's shy downstairs neighbour.
He made an inauspicious debut on the big screen in the puerile sketch film Tunnel Vision (1976), in which he played Dr Manuel Labor. He then had a small role as a non-English-speaking American footballer in Semi-Tough (1977), and starred as Barbara Hershey's psychiatrist in the dispensable horror film The Entity (1981). His first decent role came as a union leader in Mike Nichols's Silkwood (1983), which starred Meryl Streep as a nuclear plant's whistle-blower.
Nichols directed him again on Broadway in David Rabe's Hollywood satire Hurlyburly (1984-85) and he won a Tony award for his performance as a detestable Hollywood movie producer opposite Madonna in David Mamet's Speed-the-Plow (1988).
He showed a sensitive side as Anne Bancroft's devoted son in Sidney Lumet's Garbo Talks, but was suitably slimy as a record producer in Oh, God! You Devil (both 1984) and as the demented and villainous bearded stock exchange trader in Kathryn Bigelow's Blue Steel (1989), who says: "Death is the greatest kick of all. That's why they keep it for last."
However, it was Paul Mazursky's Enemies: A Love Story (1989) that allowed him one of his few romantic roles. In the New York of 1949, Silver plays a Polish Jew who escaped the Holocaust, only to have to juggle his relationships with three women. The role suited Silver's rather kinetic style of acting, as did his portrayal of Alan Dershowitz, the lawyer who defended Claus von Bulow (Jeremy Irons) against conviction for putting his wife into a coma, in Barbet Schroeder's Reversal of Fortune (1990). "You have one thing in your favour. Everybody hates you," says Dershowitz to his client.
That phrase could have referred to Silver after he seemed to betray his leftist leanings. Originally a vocal supporter of abortion, gay rights and stem cell research, an environmentalist and anti-nuclear campaigner, he changed his political orientation after 11 September 2001. At the Republican National Convention in 2004, he brought the cheering delegates to their feet by declaring: "The president is doing exactly the right thing, and that is why we need this president at this time."
After playing the boxing trainer Angelo Dundee in Ali (2001) he landed the role of the political strategist Bruno Gianelli, who moves from the Democrats to the Republicans, in 19 episodes of the liberal-leaning The West Wing (2001-06). He claimed, however, that his backing of George W Bush had lost him acting jobs.
"As for those who mock celebrity participation in politics," Silver said in an 1993 interview, "what do you want us to do? Have affairs? Become drug addicts? We have a certain visibility and power in the society. We're a celebrity-driven society. Why not use that to try to do a little good?" He was also a keen supporter of Israel.
Silver, whose 22-year marriage to Lynne Miller ended in divorce, is survived by a son and daughter.
• Ronald Arthur Silver, actor, born 2 July 1946; died 15 March 2009
