So you're a scouser?
I'm not really a football fan, most of my family are Man U, and the rest are Everton funnily enough, because my grandad is originally from Liverpool.
The bar goes up as you post, Professor Oak is just the first one, i've had a few, all the Kanto gym leaders, Orange Island, and some of the Johto.
I think they go all the way up to Sinnoh, and Serebii was adding some others, but i'm not sure what they are.