The series starred Milton the Monster, a Frankenstein-looking monster with a flat-topped, seemingly hollow head which emitted various quantities of white steam or smoke based on his mood or situation. He was created by mad scientist Professor Montgomery Weirdo and his assistant Count Kook, who lived in a haunted house on Horror Hill. Milton is a smiling, good-natured fellow, thanks to the Professor having used too much "tincture of tenderness" as explained in the opening theme of each individual Milton the Monster segment. Milton was created not of individual body parts, but rather in a mold from such liquids as "essence of terror" and "sinister sauce." Out of fear of his creation destroying him, Professor Weirdo intended to add just a touch of the aforementioned tincture of tenderness to the mold, but Count Kook bumped the Professor's elbow, resulting in too much of the tincture being added to the mix. Milton's voice, which was based on the southern accent used by Jim Nabors in his television role as Gomer Pyle, was provided by Bob McFadden who also provided voices for Professor Weirdo's resident monsters:
Heebie - a skull-faced, top hat-wearing ghoul with a Peter Lorre voice
Jeebie - a slow-witted, cyclopian, hairy green creature with a single sharp tooth that was often used to open soda cans
Professor Weirdo's nemesis was Professor Fruitcake, another mad scientist who lived in a castle on an opposite hill. Professor Fruitcake's major creation was Zelda the Zombie. Other characters in the series included Fangenstein, a biker monster apparently inspired by Marlon Brando, his sidekick Abercrombie Zombie, and Professor Weirdo's aunt, the witchy Aunt Hagatha.