The Bear King is located in Howling Mountains Northeast of Logar.
If you kill the bear when you are level 1-10 you get "Bear Master", if you are 11-19 you get "Bear Hunter" and 20+ will get you "Bear Bully"
There can be 2 bear kings spawned at once. Usually one of them spawns right where the boars and bears start to intermingle (near that big hill between the two camps), the other is on the other side of the patch near the big hill where you see the wolves and bears intermingle.
I have also seen one at the other end of the valley from the first spawn point I mentioned. I can't remember if it's a rock or a tree grouping, but you can't miss it.
Bear King will only spawn if you kill many Bears in the surrounding area.