Professor Samuel Oak (Japanese: オーキド ユキナリ博士Dr. Yukinari Okido) is a Pokémon researcher who was once a competitive Trainer, and is generally considered the best in his field.
Samuel Oak is most notable for his vast research facility, where he cares for and studies hundreds of Pokémon, including those owned by, but not currently traveling with, Trainers from Pallet Town. He has confidence in his grandson, Gary Oak, but more often joins Ash's mother and friends in cheering on Ash in his competitions.
In the novelizations written by Takeshi Shudō, Professor Oak comes from a prestigious family. He has two brothers, one is the mayor of Pallet Town and the other is the Post Master, and his grandfather was the first Trainer from Pallet Town to receive widespread recognition. According to Professor Elm, Professor Oak's studies and research mostly focus on how humans and Pokémon interact with each other.
He appears as a young boy, Sam (Japanese: ユキナリ Yukinari) in the fourth film, Celebi: Voice of the Forest. Ash befriends the young Oak, who, due to traveling from 40 years in the past, is around the same age as him. The revelation that Sam is Oak, while able to be speculated because Oak's first name was revealed in the second movie, The Power of One, comes only at the end of the movie, when Oak knows that Ash's friend's name was Sam despite Ash never telling him so, and Tracey finding the sketchbook in which young Sam drew Pikachu sleeping with Celebi in Oak's closet.
Oak lives up the road from Ash's mother and the two often appear together as they are very good friends. He currently lives with Tracey Sketchit, who became his loyal assistant in The Rivalry Revival. Tracey and Prof. Oak are very passionate about studying Pokémon and are both artists.
Dragonite is the powerhouse of Oak's. When invited to see Mirage Pokémon come to life, Oak decided to take Dragonite just in case problems arose. Problems did arise however when Professor Yung made a mirage Mewtwo that started to attack others. Dragonite was among the Pokémon who were used to try and stop it, to no avail.
Professor Oak used Pidgey when there was a contest between him and an imposter, who was actually James, on who is the real Professor Oak. Using Pidgey to attack Team Rocket, Oak muses that it's not the size of the Pokémon that determines its strength and Pidgey was the perfect example of this.
When he traveled through time, Charmeleon was one of the Pokémon that Sammy used to try and defend Celebi from The Iron Masked Marauder. Charmeleon is a powerful Pokémon that can hold its own in battle. It's current status 40 years later is unknown.