Gustave Mark Gilbert (September 30, 1911 – February 6, 1977) was an American psychologist best known for his writings containing observations of high-ranking Nazi leaders during the Nuremberg trials.

During the process of the trials Gilbert became, after Douglas Kelley,[3] the confidant of Hermann Göring, Joachim von Ribbentrop, Wilhelm Keitel, Hans Frank, Oswald Pohl, Otto Ohlendorf, Rudolf Höss, and Ernst Kaltenbrunner, among others.

Gilbert and Kelley administered the Rorschach inkblot test to the 22 defendants in the Nazi leadership group prior to the first set of trials.

[4] Gilbert also participated in the Nuremberg trials as the American Military Chief Psychologist and provided testimony attesting to the sanity of Rudolf Hess.

In 1961, when he was the chairman of the psychology department of Long Island University in Brooklyn, Gilbert was summoned to testify in the trial of Adolf Eichmann in Jerusalem.

Gilbert testified on May 29, 1961, describing how both Ernst Kaltenbrunner and Rudolf Höss tried in their conversations with him to put the responsibility for the extermination of the Jews on each other's doorstep.

The court decided not to accept Gilbert's psychological analyses of the prisoners at Nuremberg as part of his testimony.

At the time, Gilbert was serving as chairman of the psychology department of Long Island University in Brooklyn, New York.

[8] Gustave Gilbert has been portrayed by the following actors in film, television and theater productions;[9] Also, the character "Abe Fields" in Michael Koehlmeier's 2008 book Abendland ("Occident") who is based on Gustave Gilbert (see the interview with the author [10] in the Austrian paper Der Falter of 15.