I've only seen the movies, the first season and part of Johto, so here's a question for someone who's seen more: How many of Ash's pokemon change personalities when they evolve?
Butterfree, Pidgeot, and Bayleef didn't really change from what I saw, but Charmeleon turned into a rotten little cunt, but Charizard seems similar to Charmander now that he's had his ass beaten back into shape.