This film about mathematician Stanislaw Ulam is based on his autobiography with the same title but focuses only on the period of time when, as a recent immigrant from Poland, he was working on the Manhattan Project at Los Alamos.
Stanislaw Ulam is wellknown in certain academic circles, but is not a name familiar to the general public at large. His most famous contribution, aside from his work on the development of nuclear weapons, is the invention of Monte Carlo methods for numerical analysis. And the film "plays this up" by portraying Ulam as a gambler. (In my own field of soliton theory, it is his work on the FermiPastaUlamTsingou problem which is of the greatest importance and interest, but that was outside of the scope of this film.)
According to ArsTechnica, filmmaker Klein originally considered studying math himself but realized that he was less interested in mathematics and more interested in the people who do it. He is fascinated by the way the lives of Ulam and his colleague John Von Neumann differed from the stereotypes:
Quoted from
ArsTechnica
"They were throwing parties and driving fast cars, in Johnny's case," Klein told Ars. "They were so different from the math teachers I had in school."

So, the film contrasts this flamboyant lifestyle with the seriousness of their research and the horrors of World War II, and especially on the ethical questions surrounding the development of a new and terrifying weapon. 