Forbidden Worlds #21 (American Comics Group, September 1953) carries one of the most sought-after covers in the whole series: Ken Bald's giant-ant painting for "The Ant Master!", in which a professor under the mental domination of the title villain is transformed into a human ant. Dealers and auction houses routinely single the cover out as a classic piece of pre-Code monster art, and it is the main reason this number commands attention among collectors. Inside, "Letters from the Unknown!" — drawn by the veteran pulp illustrator Leo Morey — follows a couple who move into an old house and begin receiving strange, sinister post, while "The Bubbling Pit", with art by Art Gates, and "Deity of Death", drawn by Edmond Good, fill out the supernatural half of the book. "Killer's Burial" and "The Pharaoh's Ruby" complete the line-up, with Dick Beck on the lead story and Edvard Moritz also credited. Editor, as always, is Richard E. Hughes; the book is a full-colour, ten-cent newsstand comic.

Forbidden Worlds launched in July/August 1951 as a dime comic subtitled "Exploring the Supernatural!", the companion to ACG's Adventures into the Unknown — the medium's first ongoing horror title. ACG was a small, resolutely independent New York publisher founded by Benjamin W. Sangor and co-owned by Fred Iger; the corporate name on the paperwork was Preferred Publications, Inc. of Buffalo. Its horror line kept a house style distinct from the competition: atmospheric, often wry, and far lighter on gore and sexual content than the EC and Harvey books of the same year — one reason both ACG horror titles survived the 1954 Senate subcommittee hearings and the Comics Code without wholesale reinvention. The presence of Leo Morey, long a mainstay illustrator for Amazing Stories, is a good marker of the wider migration of pulp science-fiction artists into comic books in the early 1950s.

Read today, "The Ant Master!" is a textbook artefact of 1953 insect anxiety. The giant-ant premise arrived in American comics the same season Hollywood was preparing Them!, and the specific twist here — mind control turning a scientist into an ant rather than an ant growing to human scale — is a neatly perverse variation. Around it, the issue keeps up ACG's habit of putting the uncanny into ordinary settings: the mail, a new house, a piece of jewellery. Because the 1953 material is generally treated as public domain in the United States, the original issue is freely readable through Comic Book Plus and the Digital Comic Museum — while the modern restored reprints are not.