(written from a Production point of view)
Robert Ellenstein (18 June 1923 – 28 October 2010; age 87) was an actor, theater director, and acting teacher who portrayed the Federation President in Star Trek IV: The Voyage Home. He later appeared as Steven Miller in the Star Trek: The Next Generation first season episode "Haven".
Ellenstein was a longtime friend of Star Trek IV director and co-star, Leonard Nimoy. Both Ellenstein and Nimoy were early members of the Company of Angels, the oldest non-profit repertory theater in Los Angeles. One of Ellenstein's two sons, David, also appeared in Star Trek IV.
Ellenstein was born in Newark, New Jersey. His father, Meyer, was the mayor of Newark from 1933 through 1941.  Ellenstein served in the United States Air Corps during World War II and received a Purple Heart after being wounded in Holland. After his service, he attended New York University before graduating with a degree in theater from the University of Iowa.  
He began his acting career in 1947, when he joined regional theater company Cleveland Play House in Ohio.  He also directed and taught acting in Cleveland during the 1940s and 1950s.  In 1954, he moved to Los Angeles, California, where he began working in film and television.
In a career spanning four decades, Ellenstein acted in at least fourteen feature films,  five made-for-TV movies and specials, and nearly a hundred television programs. He is also noted for his extensive stage work, including numerous Los Angeles productions. Overall, he portrayed over a hundred stage roles and also directed numerous plays. 
Ellenstein was a founding member of Theatre West in Hollywood, California, established in 1962. In 1966, he co-founded the Los Angeles Repertory Company, for which he was artistic director. He was also the first artistic director of the non-profit Company of Angels, of which Leonard Nimoy and Vic Tayback were founders.   Both Ellenstein and Nimoy were honored at the Company's fiftieth anniversary in October 2009. 
Some of Ellenstein's most notable stage works include a national tour of Irma la Douce in the 1960s and a production of Hamlet at the Actors Center Theatre Wing in Los Angeles in 1988. For the latter, Ellenstein used no props and only six actors, including son David, who played Hamlet. Ellenstein was directed by his other son, Peter Ellenstein, in Rocket to the Moon at LA's Company of Characters Theater in 1992 and in King Lear with the Los Angeles Repertory Company in 1999. 
Ellenstein played several roles that were portrayed at another time by Star Trek: The Next Generation star Patrick Stewart. Besides the aforementioned King Lear, Ellenstein and Stewart have both played Ebenezer Scrooge (in A Christmas Carol), Cassius (Julius Caesar), and Vladimir (Waiting for Godot). Ellenstein also acted in and/or directed such plays as Back to Methuselah, The Comedy of Errors, Don Juan in Hell, Endgame, Fiddler on the Roof, The Glass Menagerie, On the Town, Pygmalion, and Titus Andronicus. 
Ellenstein made his motion-picture debut in the 1954 film noir Rogue Cop, which also featured Peter Brocco. Ellenstein's next two films were also of the noir genre: 1955's Illegal (with Lawrence Dobkin and Star Trek: The Original Series star DeForest Kelley) and 1957's The Garment Jungle (with Celia Lovsky).
He had a supporting role in the classic 1957 western 3:10 to Yuma, which had a score composed by George Duning. In the 1958 World War II drama The Young Lions, Ellenstein, Paul Comi and Michael Pataki all made uncredited appearances while Parley Baer and Hal Baylor had credited roles. Ellenstein then had a featured role as kidnapper Licht in Alfred Hitchock's 1959 film classic North by Northwest. This film also featured appearances by Stanley Adams, Bill Catching, Lawrence Dobkin, and Ken Lynch.
Ellenstein later appeared in the 1966 drama Deathwatch, which was produced by his fellow Company of Angels alumni, Leonard Nimoy and Vic Morrow. Nimoy and Michael Forest starred in the film, which Morrow also directed; the music was composed by Gerald Fried. Ellenstein's other film credits during the 1960s include Pay or Die (1960, with Barry Russo), King of the Roaring 20's: The Story of Arnold Rothstein (1961, assistant directed by Lindsley Parsons, Jr.), and The Legend of Lylah Clare (1968, with Lee Meriwether).
His next film role was a cameo appearance in the 1979 horror comedy Love at First Bite, which also featured Barry Gordon and the aforementioned Michael Pataki. His final film was the 1985 comedy Brewster's Millions, in which fellow Star Trek film actor Stephen Collins was a principal cast member.
Ellenstein acted in dozens of television programs throughout the 1950s, 1960s, and 1970s. He first acquired recognition for his portrayal of Quasimodo in a live airing of "The Hunchback of Notre Dame" for Robert Montgomery Presents in 1954. He performed in several more productions for Robert Montgomery, including one with William Windom in 1955.
Many other television shows have featured more than one appearance by Ellenstein. The actor performed in at least three productions of The United States Steel Hour, working with such actors as Theodore Bikel, David Opatoshu, and Nehemiah Persoff. He later appeared in three episodes of Perry Mason, including one with Leslie Parrish. In 1959, Ellenstein was directed by John Newland in two episodes of One Step Beyond.
He guest-starred in five episodes of both The Wild Wild West and Mission: Impossible. On the former, he acted with Anthony Caruso, Chuck Courtney, Michael Dunn, Sherry Jackson, Reggie Nalder, Susan Oliver, Vic Perrin, and William Schallert. Three of Ellenstein's episodes were directed by Marvin Chomsky. On Mission: Impossible, Ellenstein appeared in three episodes with Leonard Nimoy, who was a regular on the show from 1969 through 1971. Others Ellenstein worked with on the show include Arthur Batanides, Michael Bell, Victor Brandt, Stanley Kamel, Alfred Ryder, and director Alexander Singer.
Ellenstein was also a frequent guest star on The Lawless Years (starring James Gregory), The Untouchables (working with Meg Wyllie and director Vincent McEveety), and Ironside (working with Gene Lyons, John Rubinstein, Paul Sorensen, and director Leo Penn). In addition, he has appeared in two episodes of such shows as The Man with U.N.C.L.E. (including an episode with Michael Ansara), The Big Valley (with Paul Fix and Byron Morrow), Marcus Welby, M.D. (with Steve Ihnat), McCloud (working with Lou Antonio, Ken Lynch, Diana Muldaur, and Dean Stockwell), and CHiPs (with Robert Pine).
One of Ellenstein's most memorable television roles was that of the villain in the pilot episode of Moonlighting, directed by Robert Butler and co-starring Sam Hennings and Brian Thompson. Ellenstein's other notable one-off TV appearances include spots on The Rifleman (with Paul Fix), Ben Casey (with Arlene Martel), Get Smart (with Arthur Batanides), The Virginian (with John Hoyt), Mannix (with Hal Baylor, Whit Bissell, Sally Kellerman, and Jason Wingreen), Columbo (directed by Leo Penn), The Rookies (with Fred Williamson), The Rockford Files (with Sid Haig), The Bionic Woman (with Henry Darrow and Charles Lucia), Quincy, M.E. (with Whit Bissell, Robert Ito, and Garry Walberg), Hawaii Five-O (with Chuck Couch), and V (with Jeff Yagher).
Ellenstein died of natural causes in a Los Angeles nursing home on 28 October 2010. He was 87 years old. He is survived by his wife of 58 years, Lois; their two sons, David and Peter; a daughter, Jan Ellenstein-Keeva; and four grandchildren.