Wilson subsequently wrote a number of prequels, sequels and spin-offs based upon the "Illuminatus!" concept, including an incomplete pentalogy called "The Historical Illuminatus Chronicles", a standalone work entitled "Masks of the Illuminati" and "The Illuminati Papers", in which several chapters are attributed to the trilogy's characters. Many of Wilson's other works, fictional and nonfictional, also make reference to the Illuminati or the "Illuminatus!" books. Several of the characters from "Illuminatus!", for example, Markoff Chaney ("The Midget") and Epicene Wildeblood, return in Wilson's "Schrödinger's Cat Trilogy", which also carries on some of its themes. The third book of the "Cat" trilogy, "The Homing Pigeons", is actually mentioned as a sequel to "Illuminatus!" in "Appendix Mem". In 1998, Wilson published an encyclopedia of conspiracy theories called "Everything is Under Control", which explains the origins of many of the theories mentioned in "Illuminatus!".