Professor Oak (anime)/History/Diamond & Pearl series

Ash spoke to Professor Oak regularly over the phone while he traveled through the Sinnoh region. was able to recognize him from television, but it was because of his Pokémon poetry and not his research.

In Get Your Rotom Running!, Oak suggested that Ash and should visit the Old Chateau to sample its famous delicacy, the.

In Strategy Begins at Home!, Ash called Professor Oak while staying at Johanna's house and said he would be in Twinleaf Town for a while. Oak told him to use this opportunity to learn from Johanna, as her experience as a Top Coordinator could be helpful to him. Oak also announced that he would be attending the Twinleaf Festival as a special guest.

In A Faux Oak Finish!, he traveled to Sinnoh to give a lecture on "the interrelation of and Evolutionary stones" on the first day of the Twinleaf Festival. However, on his way to Twinleaf Town, his car got a flat tire and forced him to make a stop near a marshland. While the driver was replacing the tire, Oak decided to explore the area. He found a group of wild Pokémon who led him to a cave where a depressed was hiding. Oak found out why Lombre was so sad and gave it a Water Stone, allowing it to evolve into and immediately taking it out of its depressed state.

Meanwhile, in Twinleaf, James was in the town's auditorium disguised as Oak plotting to steal all of the attendees' Pokémon. When Oak arrived there, everyone in the auditorium looked confused as James insisted he was the real Professor Oak. Seeing this, a in the audience sent out his  and asked for help, saying he was having trouble with the. James failed to figure out what was the cause of the problem and was sent blasting off by Tyranitar, but Oak was able to help the Pokémon by removing a thorn from its foot. After that, Professor Oak proceeded to give his lecture.