In the quest The Heart of the World, you must defeat him.
The Lord of the Netherrealm.
In Torchlight IIEdit
In Torchlight 2, the Netherlord is the main antagonist and the lord of the Nether. He managed to break the Clockwork Core, allowing creatures of the Nether to get into Torchlight. You must defeat the Netherlord in the last main quest, The Heart of the World, in order to repair the Clockwork Core and ultimately save Torchlight.
Phase 1 Edit
The Netherlord starts off fairly easy to kill, providing you have health potions. Once you kill him, he reaches the next phase.
Phase 2EditThe Netherlord becomes significantly larger and harder to kill. His health greatly increases and he can be challenging to defeat.
When the Netherlord is defeated, he drops a variety of different items and a boss chest is accessible, with loot inside. A portal to the surface is spawned and you complete the final main quest, and unlock the Mapworks and New Game Plus.