Udyr feels... Unconnected.
 

I've noticed most champions can be connected to most other champions through complex chains of relationships, which I think is pretty cool. Even of those champions that really don't have any connection to any other champions, most demonstrate a reasonable reason for joining the league in their backgrounds.

Udyr, as far as I can tell, has no major connection to any other champion in the league, and his lore never really explains why he joined in the first place. He just feels sort of... out of place. When I look at Udyr I can't understand why he's even around, from a storytelling point of view. Unless there's something in the Journal that I've missed.

I believe he's in the League to practice maintaining his inner rage or uses it as a way of exerting it.
But you are right, he has 0 connections to anyone and he wasn't mentioned in the JoJ

Actually, he was in the Ionia vs Noxus Rematch. I'd have a long spiel, but I'm saving this spot for another day when I'm not tired and about to sleep. There are possibilities with him, lots of em. Just have to dig...incredibly friggin' deep.

I did see he was in the rematch, yes, but I'd say the connection of geography is fairly weak compared to the direct relationships some other champions have with each other.

I think that his disconnection with everyone else is one of his main character traits.

He is a loner, through and through. An anti-social, wild and primal man, the ultimate individualist.

He didn't join the League to fight for something or someone, he just joined to fight.

You don't ask why a plague spreads or a field burns. Don't ask why he fights.

He's friends with Lee Sin to my knowledge. But other than that, he's more of a gameplay character than a lore one. He fits in the lore, he just doesn't play an active part.