The Brainiac (1962)

In 1661 Mexico, the Baron Vitelius of Astara is sentenced to be burned alive by the Holy Inquisition of Mexico for witchcraft, necromancy, and other crimes. As he dies, the Baron swears vengeance against the descendants of the Inquisitors. 300 years later, a comet which was passing overhead on the night of the Baron's execution returns to earth, bringing with it the Baron in the form of a horrible, brain-eating monster that terrorizes the Inquisitor's descendants.