Professor Oak is featured in Pokémon Red, Blue and their remakes, FireRed and LeafGreen. In these games, Oak either gives the Trainer a Bulbasaur, a Charmander or a Squirtle, but in Pokémon Yellow he gives the Trainer a Pikachu.
Professor Elm is featured in Pokémon Gold, Silver, Crystal and their remakes, HeartGold and SoulSilver. In these games, Elm either gives a Chikorita, a Cyndaquill or a Totodile to the Trainer. This Pokémon lab is in New Bark Town.
Each Generation has three different starter Pokémon, all of whom are Grass, Fire or Water-type Pokémon.