Forbidden Worlds #1 is a 52-page anthology of supernatural and horror short fiction published by the American Comics Group in July/August 1951. The debut issue opens with "Demon of Destruction", in which atomic physicist Don Brady inadvertently releases Marzo, the Spirit of Destruction, who offers him three wishes in exchange for freedom — artwork split between Al Williamson (pencils) and Frank Frazetta (inks). Further stories explore werewolves, vampires, and ghostly armies: Monsieur Werewolf, Love of a Vampire, The Way of the Werewolf, Vampire's Victim, The Ghostly Army of Bethune, and The Monster Doll. The cover — a two-headed monster rendered by Ken Bald — sets the lurid, pre-Code tone that would define ACG's horror output for the next decade. Cover price: $0.10. Subtitle: "Exploring the Supernatural!"

Launched as a companion title to ACG's earlier horror flagship Adventures Into the Unknown (1948), Forbidden Worlds was published under the Preferred Publications Inc. imprint at 8 Lord St., Buffalo, NY, with editor Richard E. Hughes overseeing all creative output — often writing stories himself under numerous pen names. The series predated EC Comics' best-known horror titles and is considered one of the earliest sustained horror anthologies in American comics history. Unlike EC, ACG kept its content relatively restrained, a strategy that allowed the title to survive the Comics Code Authority crackdown in 1955 largely intact. The issue introduced the letters-column header design (no actual reader letters yet in #1) that would persist throughout the run.

Today, Forbidden Worlds #1 is a prized Golden Age key issue for three reasons: it is the first appearance of an ACG horror title that ran for 145 issues (1951–1967); it contains early work by Frank Frazetta and Al Williamson in a documented creative collaboration whose exact pencil/ink division remains debated among scholars; and it is fully in the public domain in the United States, making it freely reproducible and researchable. High-grade copies command $3,000–$4,500 at auction (CGC NM 9.4). The series won the Alley Award for Best Regularly Published Fantasy Comic in 1964.