While sieging the Orc camps near Walstow, you have heard a name snarled by the Orcs. If there is a leader of this force, it must be defeated.
You have overheard Orcs of the camps near Walstow snarling something that can only be the name of one Orc. You should defeat the leader of this force and plunge the remaining Orcs into disarray.
You have overheard Orcs of Mordor uttering a particular name - a name that can only belong to their leader. Thauk can be found deep in the Orc camp to the south of Walstow.
You have defeated Thauk and shattered the leadership of the invading Mordor Orcs.