To summon him you have to go to 66.30 31.54. There will be a green and a red circle. Someone has to stand on the green circle and do /lie and another person has to stand on the red circle and do /kneel.
After you do it he'll yell: "You wish to pay me tribute? Then pay it with blood!"
He summons some stone dogs but this guy is easy. After you kill him, collect his loot. He can be tagged by everyone and the Ashes of Warlord Gurthan can be looted by everyone. This item starts a daily quest.