Perpetual Lustre is the Duke of Glass, the exiled erstwhile leader of the Fabreal Duchy. He refused to join with the Principality and was usurped by his counts. He now resides in Joyous Guard.
Like all nobles of the Fabreal Duchy, he is made of glass through which flows the oil of Unction. The oil is what contains his selfhood, and it can be passed between bodies. Facial expressions are represented by the formation of curling whiskers of glass.
By the end of Wagon Wheel, Perpetual Lustre has been poisoned by shrimp broth after the combined efforts of the BigStar★ crew and August Righteousness. He is now ill and held under the control of the rebel Delegates.
Constantina Malady is a pretender to his title, but it is unclear if they have any relation.