Spoilers ahead
The Duke is a melancholy NPC described as “a lover, not a fighter.” He wanders Queensbury Crypt in search of a mysterious, lost love. Helping him is an optional but highly worthwhile side quest.
The Proto Spark reward
Escort the Duke to his casket inside the Crypt and he gives you the Proto Spark trinket — one of the best trinkets in the game, granting one free save from death (a revive that recharges at checkpoints). Grab it before tackling the Duchess of Queensbury boss.
The Duke and the Duchess (spoiler)
The boss The Duchess of Queensbury is described as masquerading as the Duke’s long-lost companion — an eldritch horror hinting at the corruption plaguing Tenebrous Isle. That connection is what gives the Crypt’s boss fight its implied tragic story.
FAQ
Who is the Duke?
A "lover, not a fighter" who wanders Queensbury Crypt searching for his lost love. Helping him is an optional side quest.
What do I get for helping the Duke?
Escort him to his casket in the Crypt and you receive the Proto Spark trinket — one of the best in the game, granting a free save from death.
Is the Duke's lost love the Duchess?
The boss known as the Duchess of Queensbury masquerades as the Duke's long-lost companion, which gives that fight its tragic undertone. (Spoiler.)