Professor Oak is a Generation-1 professor who gives you your first pokemon at the begining of the game in the original series. You can choose from 3 different starters:
- Charmander, a fire type pokemon. Weak against water type, strong against grass type.
- Bulbasaur, a grass poison type pokemon. Weak against fire type, strong against water type.
- Squirtle, a water type pokemon. Weak against grass type, strong against fire type.
Your Rival, Gary Oak, grandson of Professor Oak, chooses the pokemon that is strong against yours. If you chose a charmander, he will choose squirtle. If you chose squirtle, he will choose bulbasaur. If you chose bulbasaur, he will choose Charmander. He is sort of a jerk that way.
In pokemobs, he may be added in towns, but it is unconfirmed what he will do.