Outside of American Psycho
Bateman made his first appearance in Ellis' 1987 novel The Rules of Attraction (in which Sean, his brother, is the main character); no indication is given that he is a serial killer. Bateman also makes a short appearance in Ellis' 1998 novel Glamorama, with "strange stains" on the lapel of his Armani suit and Victor mentions "He has a coat-of-arms, baby".
Bateman also appeared in the American Psycho 2000 e-mails (transcribed here), which were written as an advertisement campaign for the movie. Although they are often mistakenly credited to Ellis, they were actually written by one or more unnamed author(s) and approved by Ellis before being sent out. American Psycho 2000 served as a sort of "e-quel" to the original novel. The e-mails take place in 2000, a little over a decade since the novel. Bateman is in therapy with a Dr. M. He is also married to Jean, his former secretary. They have a son, Patrick Bateman Jr. (P.B.), who is eight years old. In the story, Bateman talks about therapy, trying to get a divorce from Jean, his renewed feelings about murder, and idolizing his son. In the end, it is revealed that the 'real' Bateman, who 'writes' the e-mails, is the owner of the company that produces the movie.
Bateman appeared in Ellis' 2005 novel Lunar Park, in which the fictionalised Bret Easton Ellis confesses that writing American Psycho felt like channeling the words of a violent spirit rather than writing anything himself. This ghost—Bateman—haunts Ellis' home. A character also comes to Ellis' Halloween party dressed as Patrick Bateman, and a copycat killer is seemingly patterning himself on Bateman. Toward the novel's end, Ellis writes the 'last' Bateman story as a way of confronting and controlling the character, as well as the issues Ellis created Bateman as a means of countering. Bateman, for all intents and purposes, dies in a fire on a boat dock.
Read more about this topic: Patrick Bateman