Franz Anton Mesmer was an 18th-century German physician known for developing the theory of animal magnetism, which he believed could influence health through a magnetic fluid in the body. His practices involved using magnets and his hands to manipulate this fluid, aiming to cure various ailments. Mesmer's ideas laid the groundwork for the field of hypnosis, although his methods were often met with skepticism. Despite the controversy surrounding his work, he significantly impacted the understanding of psychological healing and the mind-body connection, influencing later figures like Sigmund Freud and the development of psychotherapy.