Creatures on the Loose #21 was published by Marvel Comics on January 1, 1973, as part of a series that began in 1971. George Alec Effinger and Larry Lieber write, and art comes from Gray Morrow, Jim Steranko and Joe Sinnott. This 36-page issue features Gullivar Jones, Heru, The Green Thing, Chak and Ar-Hap.