Fester was Morticia's uncle.
Though Uncle Fester is a regular on the TV series, Charles Addams' prototype for Fester in the New Yorker cartoons was almost exclusively solitary, never shown indoors with the other family (except once as a painted portrait), and only once outdoors with the children (going fishing with dynamite).
With the start of the TV series, The New Yorker magazine stopped running any Addams-Family-themed cartoons from Charles Addams until just prior to his death in 1988, although a few familiar characters were allowed solitary appearances (the prototypes for Pugsley, Cousin Itt, and Fester).
Cousin Itt is the only character whose name was carried over from the original New Yorker cartoons, where he was just "It".
Gomez was a lawyer.
Wednesday's pet, Homer, was a black widow spider. Her headless doll was named Marie Antoinette.
Pugsley's pet Octopus was named Aristotle.