He was best known for his work on the ABC serial Dark Shadows (1966–1971), as Dragon, the Albino ex-Nazi Director of C-2 in The Eiger Sanction (1975) and as the fight promoter Miles Jergens in Rocky (1976).

He also appeared as Count Saknussemm in the film Journey to the Center of the Earth (1959), as the Reverend Silas Pendrake in Little Big Man (1970), as Charlie Robbins in Save the Tiger (1973) and as Deacon in Fun with Dick and Jane (1977).

[1][2] He went on to act in The Relapse 1950 (Sir Tunbelly Clumsey); The Taming of the Shrew 1951 (Grumio); The Way of the World 1954 (Petulant); The Carefree Tree 1955 (The Sixth Son); King Lear 1956 (Duke of Cornwall); Mister Johnson 1956 (Gollup); Saint Joan 1956 (The Inquisitor); Protective Custody 1956 (Dr. Steidl); Oscar Wilde 1957 (Oscar Wilde); The Golden Six 1958 (Tiberius); A Man for All Seasons 1961 (Cardinal Wolsey); La Belle 1962; Andorra 1963 (pub keeper); The Seagull 1964 (Sorin); The Crucible 1964 (Danforth); Baker Street 1965 (Moriarty); The Royal Hunt of the Sun 1965 (Miguel Estete); Ring Round the Moon 1966 (Messerchann); Those That Play the Clowns 1966 (Henning); Breakfast at Tiffany's 1966 (Rusty Trawler); The Sorrows of Frederick 1967; The Bench 1968 (Phillipi); Uncle Vanya 1971 (Serebryakov); The Jockey Club Stakes 1973 (Sir Dymock Blackburn); and The Dogs of Pavlov 1974.

David appeared in TV movies such as Nikita Khrushchev in Francis Gary Powers: The True Story of the U-2 Spy Incident (1976) and The Amazing Howard Hughes (1977), as well as miniseries such as Roots, The Rhinemann Exchange, and Washington: Behind Closed Doors.

[citation needed] In 1977, David played the title role in Nero Wolfe, Paramount Television's made-for-TV movie based on the Rex Stout novel The Doorbell Rang.

[7] "He was the most widely educated and best-read actor I've ever encountered," said Frank D. Gilroy, who wrote and directed the 1977 TV movie Nero Wolfe.