Dwarven King Quest Arc
The Dwarven King Quest Arc is a series of quests written by R.A. Salvatore introduced in Module 8: Underdark. You can access these quests at level 60 by talking to Captain Belgold in Protector's Enclave. There are nine quests in total that take the players to various locales across the Sword Coast. During the quests you'll encounter characters from Forgotten Realms, including Thibbledorf Pwent, Regis, and Bruenor Battlehammer.
Completing the final quest in the Arc unlocks the Underdark Campaign for all characters on the account, and rewards the [Bruenor's Helm] Artifact. After completing the quest arc you can replay the quests to earn any missing achievements by talking to Captain Belgold.