Before you can expel this darkest of shadows, you'll have to hunt him down. For one so large, he hides quite well. It's vexing. I dislike it.
If you search for him blindly, you may search forever. So instead, call him to you. Use the voice of his lieutenants, and call out his name. Then he may appear before you, with all his wrath and fury. Then you'll have your chance.
But to speak with the voice of his lieutenants, you must take their hearts. Or if you can, take their minds, and pit their strength against his. However you do it, they are the key. You must begin with them.