This structure allowed Gaiman great scope to include various magical characters from across DC's ranges, as well as reintroducing characters that weren't currently in print. In his introduction to the collected edition, author Roger Zelazny also noted that the structure bore some similarity to the key story points of the mythic structure identified by Joseph Campbell's "The Hero with a Thousand Faces" - although he did allow that this might come from Gaiman's intimate knowledge of the same source material rather than a deliberate attempt to follow Campbell's guidelines. When the book was initially released over 1990/1991, it proved very popular and led Vertigo Executive Editor Karen Berger to make it a regular ongoing series under editor Stuart Moore.