Professor Oak (anime)/History/Original series

Professor Oak made his debut in Pokémon, I Choose You!, appearing on a late night television show explaining the three starter Pokémon that Pokémon Trainers would receive. The next day, three Trainers from Pallet Town, including his grandson, Gary Oak, came to his lab, ready to become Pokémon Trainers. Oak gave them each a Starter Pokémon, including giving Gary his, though this wasn't revealed until much later in the series. Later that same day, Ash came to him as he was also starting his Pokémon journey and needed his first Pokémon as well. But because he was so late, the only Pokémon Oak had left was a rebellious.

He appeared again in Pokémon Emergency where he called the Viridian City Pokémon Center after hearing that Ash had already made it there from his mother. He stated how he was surprised that he had made it that far, and expressed doubts he had when Ash first left. Mentioning making a bet of a million dollars with Gary that Ash hadn't captured any new Pokémon, he was disappointed to hear that this was indeed true and he had lost the bet with his grandson. When Ash told him that he had seen an unknown Pokémon, which resembled the, he waved it away as nonsense, saying that Trainers have searched their whole lives for that Pokémon, and none have succeeded.

Over the course of Ash and Gary's journeys, Professor Oak took care of the Pokémon they captured that were sent to his lab. He would often gloat about how much farther ahead his grandson was to Ash, which often caused him to be extra competitive. During the Indigo Plateau Conference, Oak became greatly disappointed when he discovered that Gary had lost in the third round, but decided to look on the bright side, telling Misty and Brock that it would do Gary good to learn that "every road, no matter how smooth, has its bumps along the way". He had arrived with Ash's mother with the goal of cheering Ash on in mind.

After the end of the Indigo Plateau Conference, Professor Oak asked Ash to pick up a mysterious Poké Ball from his friend, Professor Ivy, who lived on Valencia Island in the Orange Archipelago. He wasn't at all surprised when Ash called him asking if he could compete in the Orange League. Though he wanted to study the GS Ball, he also wanted Ash to compete in the league so that he can get more training. During Ash's adventures in the Orange Islands, he befriended a Pokémon watcher by the name of Tracey Sketchit who was a great admirer of Professor Oak. When they arrived back in Pallet Town, Tracey asked if he could become his assistant which he graciously accepted.

Not being able to discover the mystery behind the GS Ball, Professor Oak called for Ash's assistance once more and asked him to travel to the Johto region and give the Ball to his friend Kurt. He also explained that there were many new Pokémon out west which made Ash all the more eager to go and catch up with his rival, Gary.

Professor Oak traveled to Johto on a couple of occasions for conferences, most notably during Ash and Gary's battles in the Pokémon League Silver Conference.