(written from a Production point of view)
Richard Carlyle (20 March 1914 – 15 November 2009; age 95)  was the actor who played Carl Jaeger in the Star Trek: The Original Series first season episode "The Squire of Gothos". He was born in St. Catharines, Ontario, Canada. His death was reported by Star Trek: Enterprise guest star Jim Beaver on 24 November 2009. 
Carlyle was a long-time member of the Los Angeles theater company Theatre West, of which Jim Beaver is currently a member. Carlyle ran the apprentice program at Theater West for many years; one of his students was Star Trek: Deep Space Nine actress (and Jim Beaver's wife), Cecily Adams. Other Star Trek veterans who are (or were) part of the Theatre West company include Barry Jenner, Hal Lynch, Lee Meriwether, and Malachi Throne. 
Carlyle acted in many live television dramas during the 1950s, including Studio One, Kraft Television Theatre, and Playhouse 90. In his first episode of Studio One in 1950, entitled "The Last Cruise," he co-starred with DeForest Kelley nearly seventeen years before they worked together on Star Trek. This episode also featured Richard Webb, who later guest-starred in the Star Trek episode "Court Martial". Carlyle later worked with Leonard Nimoy prior to their time on Star Trek when they guest-starred together in two episodes of the western series 26 Men in 1959.
In addition, Carlyle acted alongside Richard Kiley on the live NBC anthology series The Clock in 1951. On Playhouse 90 in 1958, Carlyle worked with fellow Star Trek guest performers Tige Andrews and Celia Lovsky, as well as Star Trek: The Next Generation guest star Paul Lambert.
Carlyle made recurring appearances on various shows during the late 1950s and early 1960s, though never as the same character. He made three appearances on the crime drama 77 Sunset Strip between 1958 and 1962. He also guest-starred in two episodes of the western series Wanted: Dead or Alive, the first in 1959 (with Phillip Pine) and the second in 1961 (with Bill Quinn). In addition, he made two separate appearances on the crime drama The Untouchables, first in 1959 (in an episode with Lawrence Dobkin and Dick Miller) and again in 1961 (in a two-part episode with William Schallert).
Besides Star Trek, the other television shows on which Carlyle appeared throughout the 1960s include Dan Raven (a crime drama which starred Skip Homeier in the title role), One Step Beyond (directed by John Newland and acting with Richard Hale), Alfred Hitchcock Presents (with John Anderson), Alcoa Premiere (directed by Herschel Daugherty), The Alfred Hitchcock Hour (with William Sargent), Dr. Kildare (with Tony Dow), The Great Adventure (with Andrew Prine), A Man Called Shenandoah (with Harry Townes and Bill Zuckert), Land of the Giants (with Don Marshall), and Marcus Welby, M.D. (with Byron Morrow). He also appeared on the popular westerns Rawhide and Gunsmoke.
In the 1970s, Carlyle appeared on the television series Cannon (with Lou Antonio), Harry O (starring Anthony Zerbe), Kojak (with Andrew Robinson), Emergency! (with Kevin Tighe), and The Brady Bunch. He also had small roles in a few TV movies, including Say Goodbye, Maggie Cole (directed by Jud Taylor) and Marciano (with Richard Herd and Michael Pataki). He only appeared in two television shows during the 1980s: Brothers (in an episode with Hallie Todd) and This Is the Life (with Kim Darby, Henry Darrow, and the aforementioned Andrew Robinson). His last television work was the 1994 TV movie Secret Sins of the Father, which also featured Jack Kehler, Ed Lauter, Bert Remsen, and Mark L. Taylor.
Film and stage work
Carlyle also had many feature film and stage productions to his credit. He performed in several Broadway plays, including Mrs. Gibbons' Boys in 1949 (with Ray Walston), Out West of Eighth in 1951 (with Mary Carver), and Fragile Fox in 1954 (with James Gregory and Jason Wingreen). His first film was the 1951 war drama Target Unknown.
Carlyle's second film role was that of Rezin, the brother of Jim Bowie in the 1952 western The Iron Mistress. In 1958, he was directed by Joseph Pevney in the war drama Torpedo Run, which also featured Frank Gorshin, Don Keefer, and William Schallert. Carlyle's next film, 1960's The Gallant Hours, was also a war film with William Schallert. Ward Costello had a major supporting role in this latter production.
Carlyle had a supporting role in the 1966 detective film Harper, along with Roy Jenson. The following year, Carlyle was seen in the yacht racing drama Sail to Glory with James B. Sikking. His next and last feature film came over two decades later when he made a brief appearance in the 1990 submarine comedy Going Under. Star Trek: Voyager guest actress Wendy Schaal and TNG guest star Chris Demetral were two of the stars of this film.