Boss BoltugFollow

Anyone have any usefull details about this mob?!?

ie: how often he spawns? Is there a sure fire way to get him to spawn?

I was down the orc mines for about 5 hours the other morning (no one else was around so i know he wasnt killed by someone else) and during that time Boltugs m8 Toady Kolop only spawned once (I killed him twice)

Any ideas as I want his blade (which he doesnt drop every kill =/)