The Good, The Bad, and the Svengali
George Du Maurier wrote "Trilby" in 1894, which is sometimes referred to as the first bestseller (Hypnotism.org). It chronicled the villainy of Svengali, an evil hypnotist who could control minds and turned his assistant into his own slave.
This novel reintroduced some of the original fears of hypnosis by the public. It preyed on the feelings of losing control, and while hypnosis was and has never been used by mind control, the image of Svengali helped promulgate this image to the public and hurt the field of hypnosis for a long time. Hypnosis can't be used for mind control, as doctors insist that all patients still have their free will when in a trance. But the fear of the unknown is strong, and since many people have never undergone hypnosis, and at the turn of the century, hypnosis was far from a legitimate profession and practice, the specter of Svengali loomed large on the field of hypnosis.
To be fair to Maurier, Svengali and his novel spoke to some of the unethical hypnosis practices that DO exist. When Mesmer first came up with animal magnetism/mesmerism, it inspired a strong following from occult groups, who treated it as a magical phenomenon. It also led to stage hypnotists as entertainers. These acts are largely planned or a sham, and with Svengali, this image was hard to shake. Even today, it's good to be reminded that some hypnotherapists aren't certified or experienced before seeing one for yourself.
The death of Ella Salamon in 1902 while under a hypnotic state also caused a stir (Hypnotism.org). The Journal of the American Medical Association addresses the incident, and while it found that Ella clearly died while under a hypnotized state, it also determined that the fact that hypnosis caused the death is "questionable" at best (JAMA). Either way, the damage was done, and another roadblock to making hypnosis legitimate appeared.
This, coupled with the rise of psychoanalysis in the 20th century, helped push back hypnosis decades from clinical use (Hypnosis Black Secrets). Until Erickson melded therapy, psychoanalysis, and hypnosis together, psychoanalysis and hypnosis were seen as completely separate spheres with a rift between them.
In 1931, a popular movie based on Maurier's novel "Trilby" entitled "Svengali," starring John Barrymore, was released. The movie won two awards and is seen as one of the harbingers of the emerging horror genre in Hollywood; it is still a respected piece of art today (Robert Hood). Svengali has seen many different film and TV interpretations in Hollywood and beyond since his debut in 1894. The evil hypnotist obviously put a spell on his audience as much as his assistant -- for good or bad.