The Church of Claudandus (otherwise known as the Claudandus Sect) is a religious cult widespread among the cats of Francis's city at the time of the first book (and movie) of Felidae series.
The cult has been designed by Joker and Claudandus to create a tool to keep the minds of the other cats busy and not let the murderers caused by the breeding program for the Felidae to be on public domain.
The other main and more important intent was to prepare the feline population before the revelation of the Felidae breed that, according to Claudandus' plans, had to be the ones to overthrow humanity.
With the death of Joker, the cult suffered the sudden loss of the only priest. Joker's death has never been of public knowledge and, at the end of the first novel, the cats believed Joker to have been the murderer.
The cat was also believed to be escaped, to spread his cult in other places.
With the death of Joker and Claudandus, the Felidae breed was quickly adapted into a normal life and the cult of Claudandus was soon abandoned.
Claudandus (secret founder and god)
Joker (leader and high priest of the cult)
Jesaja (indirect member; Keeper of the Dead)
Bluebeard (admitted of being a member as "tool to chase away boredom")