Virile and good-humoured, William Sylvester was always good company in the films in which he starred, and he made more of the role of Dr Heywood Floyd in 2001: a Space Odyssey (1968) than was probably the intention of the film's director, Stanley Kubrick. The cast was made up of actors rather than stars, and the spellbinding special effects of the film's middle section aboard a space station orbiting the Earth created a sense of wonder in audiences that subverted Kubrick's bleak conception of a world in which human beings had become an increasingly small and insignificant component. Investigating a mysterious monolith discovered on the moon, Dr Floyd later made the journey to Jupiter himself in Peter Hyams's sequel 2010 (1984), in which Floyd was played by Roy Scheider: it was a much murkier film that could have done with Sylvester's relaxed and reassuring presence.
Sylvester's first appearance on the stage had been in his home town of Oakland in 1941, before joining the US Navy for the duration of the Second World War. In 1947 he settled in England to study at RADA, taking his first London bow in 1948 as the shadow in Winterset at the New Lindsey Theatre. His film dbut followed with a supporting role in Give Us This Day (1949), set amid Brooklyn's Italian community, which he followed with J. Lee Thompson's The Yellow Balloon (1952), a rare villainous part, but one in which he was well cast, calling for an actor engaging enough to take in the unsuspecting adults (one of whom was played by Veronica Hurst, who became his second wife), while able swiftly to turn on the menace with the boy hero, Andrew Ray. Sylvester also combined these qualities as Gordon Lonsdale in Ring of Spies (1964), a fictionalisation of the Portland spy case in which he was affability itself while luring Harry Houghton and Ethel Gee (Bernard Lee and Margaret Tyzack) into passing secrets to the Russians.
Sylvester played wisecracking Yanks with names like "Mac" and "Texas" in a couple of the ubiquitous war films of the Fifties, Appointment in London and Albert RN (both 1953) and a member of the Nova Scotian lobster- fishing community in High Tide At Noon (1957). On the radio he gave a fine interpretation of the title-role in The Great Gatsby, while on stage he played Captain Fisby for two years in The Teahouse of the August Moon, and made his first appearance in New York as Rudbeck in Mr Johnson in 1956. In 1961 he appeared in The Andersonville Trial at the Mermaid Theatre and as Adam Brant in Mourning Becomes Electra at the Old Vic.
By the early Sixties he was established as a rugged leading man in low- budget thrillers and horror movies, some of them quite good, such as Eugne Louri's Gorgo (1960) and Lindsay Shonteff's Devil Doll (1964), the latter a bizarre extrapolation from the ventriloquist's dummy episode in the 1945 film Dead of Night. In 1968 Sylvester returned to the US, where his television appearances included a regular role in the mediocre series Gemini Man, starring Ben Murphy as a special agent who could become invisible. His film roles became regrettably scarce and inexplicably brief, consisting of a handful of fleeting appearances in such films as The Lawyer (1970), Busting (1974), The Hindenburg (1975, as a German officer), Warren Beatty's Heaven Can Wait (1978) and First Family (1980).