The Fall of Gruul: Defeat Gruul Quest
In order to make this quest, you have to either have done Yorick the Grave Digger’s Quests first, or have someone that have done those quests to open the teleport of the rocks in Dredmor for you.
To kill Lord Dredmor you'll need level 200. This is not a part of the quest, however.
Go back to Quests.