Wrestler Brett Carson obtained super strength and used it to fight crime. He was assisted by sidekicks Kid Muscles and Miss Muscles, who appeared in backup stories. With a superhero costume consisting of red-and-black wrestling tights with a yellow "M" insignia, the blond-haired hero is one of few who did not wear a mask and whose identity is publicly known. An additional character, Steeplejack, starred in a backup feature in the second issue.
The comic book, Mr. Muscles ran two issues numbered #22-23 (March & Aug. 1956), the series having taken over the numbering of the comic Blue Beetle. The sole other known appearance of a character by this name was alongside other guests in writer-artist Steve Ditko's Creeper backup story, "Beware Mr. Wrinkles", in DC Comics' World's Finest Comics #254 (Jan. 1979).