Sigmund Freud's Moses and Monotheism (published in 1939 by Knopf) is a collection three essays in which Freud questions if Moses is in fact Jewish. Specifically, he claims that Moses is Egyptian. Freud freely acknowledges that this is a bold undertaking, but, as this was his last published book, Freud had established himself not only as an important psychologist but also as a resolute atheist.
Freud begins by citing scholars who have noted that the name "Moses" is an Egyptian name, which means something generic such as "Amon-given-child." Freud then relies on the work of his contemporary Otto Rank, The Myth of the Hero's Birth, which observed several traits common to such stories of cultural leaders (such as being fathered by parents of high station but challenging circumstances, being raised by animals at some point, the injunction that the child be killed, and the child's standing up against his father).
Freud remarks that the example of Moses stands apart from this. First, his family is a modest Jewish family. Freud proposes that Moses was Egyptian by birth. Freud reasons that the Egyptians would have no motive to glorify Moses, and so the Jews must done so in order to give their identity cultural purpose.
Moses, Freud argues, was a charismatic "Great Man" whose persona and ideas were celebrated among the Jews. Moses escaped from Egypt after the rule of the renegade Pharaoh Akhenaten (famous for proposing a replacement of the Egyptian pantheistic worship, centered on death, with the worship of one god, Aten). Freud suggests that Moses was a follower of Aten and was a cultural leader of Jews in Egypt (this timeline is consistent with Biblical events, with the primary difference that Moses is ethnically Jewish in the Bible). Freud proposes that Moses tried to teach the Jews this religion of Akhenaten, and was murdered by his own people. Regret after this murder is the source of the Jewish expectation of the Messiah.