Sir Purssefus or Purrsy (Frank Welker) for short, is Betty's mother's spoiled, surly, beloved Siamese cat. She lavishes him with attention and treats him like he’s Betty’s younger sibling. And just like any other spoiled rotten little brat, Purrsy is petty, jealous and conniving. Purrsy has accidentally accompanied Betty on one of her missions, but being a cat has not said anything about it. He tends to cause trouble, but the trouble often backfires on him. He also seems to enjoy the company of Maximus I.Q.. Maximus in turn quickly grew fond of him upon first meeting him.
- Purrsy was portrayed as a "normal" house cat in the show's first and second seasons. He has since gained the ability to speak in a French suave accent in the show's third season starting with the episode, If The Shoe Fits....; in that same episode, he breaks fourth wall.
- Purrsy was being portrayed as a "normal" house cat once again throughout the show's revival onward, but most of the time. He will also speak in a French suave accent in some episodes of the show's upcoming revival as well.
- On some occasions, Purrsy tends to fake illness, to have either Betty or Miss Barret do his bidding. Even though Betty knows that he is, however as for her mother, still douts it.