I've camped this Minotaur Hero twice for the Shackles and i'm getting pretty used to it now. I've seen many players killing everything on sight to make him spawn and I did this myself but it was useless. I made him spawn in about 20 to 25 minutes after I came each time by killing the first minotaur at the entrance of the cave.
As soon as the first mino is dead, run as fast as u can to the hill on the other side of the entrance, he spawned for me here twice, just on the left of the big wheel. The Hero begins then to wander near the wheel.
Dont want to say it's a rule but I killed Meldrath just before seeing the Hero. The first time, it was the next mino kill after Meldrath was dead and the second time, the second mino made the hero spawn. It's maybe a trigger or something but if u can handle Meldrath, give it a try.