In addition to his accomplishments on Broadway and in Hollywood, Lewis' greatest and longest lasting contribution to American theater may be the role he played as one of the foremost acting and directing teachers of his day.

Formed by Harold Clurman, Lee Strasberg and producer Cheryl Crawford, The Group was an ensemble of passionate young actors, directors and writers who came together to explore the inner processes of theatre craft.

Lewis and other members of the Group, such as Stella Adler and Elia Kazan, were proponents of a new form of acting based on the techniques of Russian director Constantin Stanislavski.

Lewis appeared in several original Group Theatre productions in the 1930s including Sidney Kingsley's Pulitzer Prize-winning Men in White and Clifford Odets' plays Waiting for Lefty, Awake and Sing!, Paradise Lost and Golden Boy.

Some of the other artists who summered there were; Elia Kazan, Harry Morgan, John Garfield, Lee J. Cobb, Will Geer, Clifford Odets, Howard Da Silva and Irwin Shaw.

In his book Slings and Arrows: Theater in My Life, Lewis complains that "being short and round", he reluctantly had to accept that, as an actor, he fell into the character, rather than the leading man category.

He played German officers, such as Colonel Pirosh in Paris After Dark (FOX, 1943), opposite George Sanders, and Sergeant Schmidt in Son of Lassie (MGM, 1945), starring Peter Lawford, Donald Crisp and June Lockhart.

He became French collaborationist Maurice Bonnard in Tonight We Raid Calais (FOX, 1943), and the villainous Japanese Colonel Sato in Dragon Seed (MGM, 1944), starring Katharine Hepburn.

Robert Lewis did return to New York in 1947 to direct his first big commercial success on Broadway, Alan Jay Lerner and Frederick Loewe's whimsical musical play Brigadoon.

Lewis taught classes for advanced members with emphasis on inner action or intention, while Kazan, who preferred to work with the younger actors, held forth on technique exercises such as sensory recall, imagination and improvisation.

In the first year alone, Robert Lewis' group, meeting three times a week, consisted of Marlon Brando, Montgomery Clift, Mildred Dunnock, Jerome Robbins, Herbert Berghof, Tom Ewell, John Forsythe, Kevin McCarthy, Karl Malden, E. G. Marshall, Patricia Neal, Eva Marie Saint, Beatrice Straight and David Wayne, to name a few.

Lewis eventually left The Actors Studio over differences with Kazan and Crawford involving the production of a play (later resolved) and a desire to concentrate on his burgeoning directorial career on Broadway.

The Actors Studio, which is still active today, became one of the leading centers for the Stanislavski System, or Method, of dramatic training, producing some of the most influential performers in American theatre and film in the later half of the 20th century.

Among the plays directed by Robert Lewis were: My Hearts in the Highlands (1939) by William Saroyan; Brigadoon (1947) by Alan Jay Lerner; Regina (1949); The Happy Time (1950); An Enemy of the People (1950); The Grass Harp (1952); The Teahouse of the August Moon (1953), winner of the Tony Award for Best Play and New York Drama Critics' Circle Award for Best Director; Witness for the Prosecution (1954) from Agatha Christie; Mister Johnson (1956); Jamaica (1957); The Hidden River (1957); Handful of Fire (1958); Chéri (1959); Kwamina (1961); Foxy (1964); Traveller Without Luggage (1964); On a Clear Day You Can See Forever (1965); and Harold and Maude (1980).

On the stage of the Playhouse Theatre in New York City, at 11:30 p.m. on the evening of Monday, April 15, 1957, Robert Lewis presented the first of eight lectures to professional actors, directors and playwrights on the subject of what, exactly, Method acting is and is not.

In his lectures, Lewis maintained that by using their voices properly, Method actors could not only master formal ways of speaking, such as required for Shakespearean blank verse, but could create much more believable characters by doing so.

After Method — or Madness?, Robert Lewis wrote two other books on acting, Advice to the Players (Harper & Row, 1980), an actors handbook, and Slings and Arrows: Theater in My Life (Stein and Day, 1984), a memoir.