The gym leaders (and by extension, the Elite Four) always seemed like the ultimate authority in both the show and in the games.  They may not have interacted with one another very often, but by virtue of being the "best" in their respective types they wielded a power that only a rare few can aspire to each generation.  While this doesn't apply to Gen I and II, later generations revealed that the gym leaders actually scale themselves down to the challenger's threat level, to provide a challenge while still giving them the opportunity to succeed.  Later on you can fight the leaders again, but with their<em>real</em>parties, which generally includes some really damn high level pokemon that are the apex of whatever type each leader specializes in.<br/><br/>I think my favorite gym leader would have to be Blaine.  There's just something about an old coot living in the middle of a volcano thinking up trivia questions all day that strikes me as hilarious.