The Forgotten Temple of Tharizdun
Gru is from a goblin tribe called the Blood Reavers. They were converted to the Cult of the Elder Elemental Eye and most were transformed in norkers. Weak and cowardly even to goblin standards, Gru was considered unworthy to go through the norker transformation, and was kept as a servant by the cult. He was captured by the Company of Wolves in the Halls of the Fallen.