Enter the dungeon

You walk through the door and find yourself in a new room. In the middle stands a man. He’s covered in a black cloak and all his facial features are obscured. In fact nothing is visible except for his cloak. The person notices you and suddenly a voice comes out of his cloak “Answer my riddle and the door before me will open to you and the treasure you desire will be one room closer” The man's voice is deep and gravely as he tells you his riddle “You measure my life in hours and I serve you by dying, what am I”

A candle

A house

A servant

I dont know