He first appeared in Curse of the Blair Witch (1999) as an old man on death row giving his last interview before being executed for the murders of seven children, in which he was portrayed by Frank Pastor.
Created by Haxan Films, the character has subsequently been represented in various other media, including novels, video games, and comic books.
For instance, several character names are near-anagrams: Elly Kedward (The Blair Witch) is Edward Kelley, a 16th-century mystic, and Rustin Parr, the fictional 1940s child-murderer, began as an anagram for Rasputin.
Rustin first appeared outside of the film in the dossier written by DA Stern, produced to further promote The Blair Witch Project.
More of Rustin's backstory is learned in The Blair Witch Files: The Dark Room which was published in August 2000, when Laura Morely and Cade Merrill venture to the ruins of the Parr house, but through Laura's eyes and her camera the house is perfectly intact.