From Bulbapedia, the community-driven Pokémon encyclopedia.

A Pokémon Professor (Japanese: ポケモン博士) is considered an expert on Pokémon in his or her respective region. Pokémon Professors are often researchers as well, and many times they are the ones responsible for distributing Pokédexes and starter Pokémon to new Pokémon trainers.

Professors from the regions showcased in the main series of Pokémon games are all named for trees.

According to a comment Professor Birch makes when grading a players Pokédex, catching a large number of Pokémon species helps to qualify one as a Pokémon Professor.

List of Pokémon professors

• Professor Oak of the Kanto region
• Professor Ivy of the Orange Islands
• Professor Elm of the Johto region
• Professor Birch of the Hoenn region
• Professor Krane of the Orre region
• Professor P of the unnamed region featured in Pokémon Trozei
• Professor Hastings of the Fiore region
• Professor Rowan of the Sinnoh region

Pokémon Professors
Oak | Elm | Birch | Rowan
Ivy | Krane | Hastings

Generation I-introduced trainer classes
Beauty | Biker | Bird Keeper | Black Belt | Boss | Bug Catcher | Burglar | Champion | Channeler | Cooltrainer Cue Ball | Elite Four | Engineer | Fisherman | Gambler | Gentleman | Hiker | Jr. Trainer♂ | Jr. Trainer♀ | Juggler Lass | Leader | PokéManiac | Trainer | Psychic | Rival | Rocker | Rocket | Sailor | Scientist Super Nerd | Swimmer | Tamer | Youngster
Beta classes
Chief | Pokémon Prof.