Sigmund Freud was a pioneering psychoanalyst who developed many influential theories about the human mind and psychology. As a young man, he studied medicine and worked as a surgeon, dissecting hundreds of eels to learn about their anatomy. He later focused his work on studying male hysteria and developing psychoanalysis. Freud faced criticism early in his career but continued his research and writing, developing over 150 theories about human psychology. He remained dedicated to his work throughout his life and career.