Too Long; Didn't Read
Professor Oak is the first actual character many people have seen in the main games. He was the first, and so far only, true “jerk” rival in the franchise, with Bede from Sword and Shield coming very close. Professor Oak was a jerk rival who left Silph co. under Team Rocket control after losing to you there. He has a (negative) dynamic with Agatha of the Elite Four, but at one point, they were colleagues in the field of Pokemon Research (at least in the Adventures Manga)