The founders, as well as the actors in the group, "tended to hold left-wing political views and wanted to produce plays that dealt with important social issues.

[6] During those years, the Group's members included Luther, Luther's sister and brother, Stella Adler and Jay Adler, Elia Kazan, John Garfield, Paul Green (playwright), Howard Da Silva, Harry Morgan (billed as Harry Bratsburg), Franchot Tone, John Randolph, Joseph Bromberg, Michael Gordon, Will Geer, Clifford Odets and Lee J.

[11] He also appeared in Kurt Weill's anti-war musical Johnny Johnson (1936)[12] and originated the role of Captain Joshua in the 1939 Group Theater production of Thunder Rock.

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.

He guest-starred in 1960 in the science fiction fantasy series, The Twilight Zone as the poor pawnbroker Arthur Castle, with Vivi Janiss as his wife Edna, in the episode entitled "The Man in the Bottle" (again appearing as Hitler).

[14] Adler is a character in Names, Mark Kemble's play about former Group Theatre members' struggles with the House Un-American Activities Committee.

[15] Adler died at his Kutztown, Pennsylvania home,[1] and was buried in Mount Carmel Cemetery, Glendale, New York, next to several of his relatives, including his parents and older sister Stella.