- Pikachu. The mascot, the icon, spawner of a dozen clones and imitators.
- Eevee. Progenitor of branched evolution, popular, cute.
- Ditto. Sure, in the original gen it's just a gimmick. And in the later gens it's just a gimmick... but a very different gimmick. Easy mode for breeding for people who don't want to research.
- Magikarp. Patron saint of evolution. Gets their own songs, games and minigames. It never misses appearances.
Honourable Mentions: The obligatory Charizard and Mewtwo mentions, Psyduck.