Ellenstein also had more than 20 film roles, appearing in "North by Northwest" in 1959 and "Star Trek IV" in 1986, and a long television resume that began in the mid-1950s.
He was the first artistic director of the Company of Angels, co-founder and artistic director of the Los Angeles Repertory Company and a founding member of Theatre West in Hollywood.
The Company of Angels, a longtime nonprofit professional theater in Los Angeles, recently honored him as part of its 50th anniversary.
One of Ellenstein's most notable Los Angeles productions starting in the late 1980s was his staging of "Hamlet" using only six actors and no props.
David Ellenstein, who played Hamlet, said his father's direction was memorable because of "the accessibility and clarity of the production. It glorified the actor and the words."
Robert Ellenstein was born June 18, 1923, in Newark, N.J., where his father, Meyer, was mayor from 1933 to 1941. Ellenstein attended New York University and graduated with a degree in theater from the University of Iowa. He also served in the military during World War II and was wounded in Holland, his son said.
Ellenstein's career started with the Cleveland Play House in 1947. By the time he moved his family to Los Angeles in 1957, he was appearing on such television shows as "The Philco-Goodyear Television Playhouse" and " Robert Montgomery Presents."
In the 1960s, his stage work included co-starring with Juliet Prowse in the national tour of "Irma La Douce."
Ellenstein directed and was directed by his sons. David is artistic director of the North Coast Repertory Theater in Solana Beach; Peter is artistic director of the William Inge Center for the Arts in Kansas.
"I don't feel any extra pressure with him here," Peter Ellenstein told The Times in 1992 during a production of "Rocket to the Moon," in which he directed his father. "A lot of what I do is based on what I learned from him."
In 1999, Robert Ellenstein played the title role in "King Lear" for the Los Angeles Repertory Company with Peter Ellenstein directing. Philip Brandes, writing in The Times, said Ellenstein "renders Lear's dark journey with admirable clarity."
In addition to his sons, Ellenstein is survived by his wife of 58 years, Lois; daughter Jan Ellenstein-Keeva of Evanston, Ill.; and four grandchildren.