The Dehumanizer is a hypnotic ray machine that can turn people into obedient zombies. Ming the Merciless uses his Dehumanizer in Chapter 102: The Tunnel of Terror of the 1936 Flash Gordon serial to force Dale Arden to marry him. As Ming explains to Dr. Hans Zarkov, "Science will overcome all things... even the human emotions."
The duration of the ray's hypnotic spell can be adjusted; it's dangerous if the spell lasts for too long.
Despite the danger, the Dehumanizer doesn't need a trained operator; the High Priest uses the machine to hypnotize Dale.
In the comic strip, the Dehumanizer is operated by a doctor. Ming informs Dale that under the ray's influence, she'll become "coldly scientific and ruthless", with no feelings of "kindness, pity or mercy". However, Ming is interrupted by a report on the Spaceograph that the palace is under attack by the Lion Men's Space Gyros. It's not clear whether Dale is ever subjected to the Dehumanizer's ray, or what effect the ray may have had. ("Flash Gordon (comic strip)")