Which incredible mastermind worked together with Sigmund Freud to compose the 1933 book Why War?

The mastermind that worked with Freud was Albert Einstein, a German-born theoretical physicist that in 1931, the Institute for Intellectual Cooperation invited to a cross-disciplinary exchange of ideas about politics and peace with a thinker of his choosing. Einstein choose Sigmund Freud despite of being skeptical of psychoanalysis he came to admire Freud's work and working with him.

The realization of the book was mainly based on a series of letters were they discussed the abstract generalities of human nature and the potential concrete steps for reducing violence in the world. This entire work was published in 1933. Only 2,000 copies of the English translation were printed, most of which were lost during the World War II. But some of the correspondence are part of the 1960 volume Einstein on Peace.