Mr. Robbins, who had a long, saturnine face and dark hair and eyes, made his Broadway debut in 1963, playing a doctor in One Flew Over the Cuckoo's Nest and made his final appearance in 2000's James Joyce's The Dead. In between, he logged in 16 Broadway plays and musicals. His busiest period was the 1970s, when he played Herbie opposite Lansbury in the 1973 production of Gypsy, probably the actor's most famous credit. He also starred with John Lithgow in several British plays, including The Changing Room (1973) and Comedians (1976) and was directed by Lithgow in one, Boy Meets Girl (1976). He replaced David Ogden Stiers in the cast of the long-running Doug Henning musical The Magic Show.
He acted in Arthur Miller's A Memory of Two Mondays in 1976 and in the 1984 Harold Prince-directed flop Play Memory.
Off-Broadway, he appeared in Urban Blight at Manhattan Theatre Club, The Dining Room at Playwrights Horizons and Henry IV, Part I at the Public Theater.
On the big screen, Mr. Robbins played Roger Sherman in the 1972 film version of "1776." His final film was "The Royal Tenenbaums."
In 1984, he co-starred with Lansbury once more, as a guest star on the television series "Murder, She Wrote."
Rex Robbins was born in Pierre, South Dakota, on March 30, 1935. He is survived by his wife and three children.