Zemocles spends most of the first movie being a villain. He is Buttinthole's sidekick and he lives, um, in her vagina. She sends him out to attack Fat Minister a few times and one time he kills some innocent bystander lady.

At the end of the movie, though, he gets mad at Buttinthole for beating up Wisegay because he is "his great ancestor" (because they're both cats, I guess) so, after Wisegay transfers some powers to him, Zemocles beats up Buttinthole and knocks her over to the vicinty of her home planet. Then he and Wisegay and the rest of the heroes' push her back into her tomb.

Zemocles is now joined with the rest of the heroes from this point on. It's that easy!