The Illearth Stone is a bane of terrible evil lurking in the depths of Mount Thunder. Drool Rockworm is said to have been searching for it in The First Chronicles of Thomas Covenant. After the recovery of the Staff of Law and death of Drool, the Stone fell into Lord Foul's possession, as he originally intended. With the power of the Stone, Foul was able to corrupt Bloodguard to his service, mutate the creatures of the Land in his grasp and awaken the Lurker of Sarangrave Flat.