Luther Adler (May 4, 1903 - December 8, 1984) was an American actor best known for his work in theatre, but who also worked in film and television. He also directed plays on Broadway.

Born Lutha Adler in New York, New York, Adler was one of six children born to Russian Jewish actors Sara and Jacob P. Adler. His siblings also worked in theatre; his sister Stella Adler achieved fame as an actress and drama teacher.

Adler made his first acting appearance on Broadway in 1921 and appeared in several productions before joining The Group Theatre in 1931. He played opposite Katharine Cornell in Alien Corn (1933), his sister Stella in Gold Eagle Guy (1934), Awake and Sing! and Paradise Lost (both 1935), and Frances Farmer in Golden Boy (1937). He also appeared in the anti-war musical Johnny Johnson (1936). By the early 1940s he was also directing but his first production They Should Have Stood in Bed closed after only eleven performances in 1942. His next directorial venture, A Flag is Born, ran for 120 performances in 1946 and featured newcomer Marlon Brando in one of the major roles.

From 1937 Adler appeared also in films, though they were never his highest priority. His credits include D.O.A. (1950) M (1951), Voyage of the Damned (1976) and Absence of Malice (1981). He also acted frequently on television, in such series as General Electric Theater, Kraft Television Theater Robert Montgomery Presents, The Twilight Zone, The Untouchables, Ben Casey, 77 Sunset Strip, Mission: Impossible, Hawaii Five-O and The Streets of San Francisco.

Adler was married to actress Sylvia Sidney from 1938 until 1947, and father of Sidney's only child, her son Jacob, who predeceased her.

He died in Kutztown, Pennsylvania, and was buried in Mount Carmel Cemetery, Glendale, New York, next to several of his relatives, including his older sister Stella.

The actor and Broadvway director Luther Adler was born into a Yiddish theatrical dynasty. One of the six children born to Jacob P. and Sara Adler, he made his debut in the world in New York City on May 4, 1903, originally billed as Lutha J. Adler. His full siblings Charles, Jay, Julia, and Stella (the famous acting teacher) as well as his half-siblings Celia and Abram Adler all appeared on Broadway, and his father Jacob, the biggest star of the Yiddish-language theater, was considered one of the great American actors. The Yiddish theater was an important cultural venue in the days when the millions of Jewish immigrants in the greater metropolitan New York area spoke Yiddish as their first (and sometimes only) language. People who trained and appeared in the Yiddish theater were instrumental in the development of the modern American theater and film, and some, including Sidney Lumet, are still active in the 21st century. It was in this cultural milieu that Luther and his siblings got their grounding in acting and the theater. Jacob Adler owned and operated his own stage in New York's Lower East Side, and Luther began appearing in the family productions at the age of five with the Adler production of "Schmendrick." He made his official debut as an actor at the age of 13 at his father's theater and his Broadway debut at the the age of 18.  Billed as Lutha Adler, he appeared in the Provincetown Players' production of Theodore Drieser's "The Hand of the Potter" in December 1921 at the Provincetown Playhouse, Adler's first Broadway hit was "Humoresque" in 1923, and he appeared regularly in top productions throughout the '20s, including "Street Scene" (1929) and "Red Dust" (1929). Along with his sister 'Stella Adler", Luther Adler was one of the original members of the Group Theatre acting company, which was formed in 1931 by Harold Clurman (his future brother-in-law), Cheryl Crawford, and Lee Strasberg. Others who would make their bones in the company were Elia Kazan, Julius "John" Garfield, Howard Da Silva, Franchot Tone, John Randolph, Will Geer, Clifford Odets and Lee J. Cobb. The Group Theatre was dedicated to bringing realism to the American stage and was instrumental in introducing the Stanislavsky technique into American acting. Most members were leftists if not communists, and the collective wanted to produce plays dealing with social issues. For the Groupe Theatre, Adler appeared in "Night Over Taos" (1932), "Success Story" (1933), "Alien Corn" (1933) and two seminal works of the American stage written by Odets: "Awake and Sing!" (1935) and "Golden Boy" (1937). He played opposite leading ladies Katharine Cornell in "Alien Corn" (1933), his sister Stella in "Gold Eagle Guy "(1934), "Awake and Sing!" and "Paradise Lost" (both 1935), and Frances Farmer in "Golden Boy" (1937). His appearance as the urban ethnic boxer Joe Bonaparte in Odets' "Golden Boy" arguably was his greatest role, but when the film was made in 1939, he was passed over for the improbably cast Wlliam Holden, a white-bread WASP. Although Adler appeared in many motion pictures, his reputation would remain primarily that of a stage actor. Adler became a director on Broadway in 1942, though his first staging, "They Should Have Stayed in Bed", was a flop, lasting but 11 performances. He next directed Ben Hecht (I)'s pro-Israel propaganda play "A Flag is Born" in 1946, starring the great Paul Muni (I), a graduate of the Yiddish theater, and newcomer Marlon Brando, an Irish-American born-Protestant who had been trained by his sister Stella. The play, which raised money for Jewsh refugees from the Holocaust seeking sanctuary in Palestine, was a hit, running for 120 performances. He also directed "Angel Street" (1955) and "A View from the Bridge" (1960). He last appeared on Broadway as a replacement in the long running "Fiddler on the Roof." Adler made his movie debut in 1937 with "Lancer Spy," but he never became a star in that medium. His best roles like "Golden Boy" and "Humoresque" were taken by other actors, including Group Theatre alumnus John Garfield (I). He had memorable supporting turns in the noir classic "D.O.A." (1950), in Joseph Losey's remake of "M "(1951), in Paul Muni's last film "The Last Angry Man" (1959), in the Holocaust drama "The Man in the Glass Booth" (1974), and as Paul Newman's mobster uncle in "Absence of Malice" (1981). He also worked frequently on television. From 1938 until 1947, Adler was married to the actress Sylvia Sidney. They had one child, a son, Jacob. Luther Adler died in Kutztown, Pennsylvania on December 8, 1984. He was 81 years old.