A113 and its variants are an inside joke and Easter egg in media developed by alumni of California Institute of the Arts, referring to the classroom used by graphic design and character animation students.
Students who have used the classroom include John Lasseter, Tim Burton, Michael Peraza, and Brad Bird. It has appeared in several Disney films and almost every Pixar movie.
Brad Bird first used it for a license plate number in the "Family Dog" episode of Amazing Stories: "I put it into every single one of my films, including my Simpsons episodes—it's sort of my version of caricaturist Al Hirschfeld's 'Nina'."[1] It also appears in South Park, Aqua Teen Hunger Force, Family Guy, American Dad!, Doctor Who and the SPA Studios animated film Klaus (2019). The first Disney movie Bird used it in was The Brave Little Toaster (1987), in which he worked on as an animator.[2] It can be seen as The Master's apartment address when Toaster and his friends knock on the door. It also appears in on an agent's poison ring and in the script when Ethan Hunt requests evac at rendezvous point Alpha 113.
Another reference is in The Truman Show when all the cameras on Truman's set are shown and one is labeled A113 but it is not confirmed whether it is a real reference or just a coincidence.
The series finale of the children's show, Arthur, features a door labeled "A-113."