Mercurius

Name: Mercurius
Age: At least 30,000-40,000

The Mercury (水銀, Suigin), better known as King of Mercury: Mercurius (水銀の王メルクリウス, Suigin no OuMerukuriusu) or Karl Ernst Krafft (カール・エルンスト・クラフト, Kāru Erunsuto Kurafuto) is the Fourth Heaven and an overarching antagonist in Dies Irae.

Mercurius is a androgynous man with long dark blue hair. He is noted to greatly resemble both Ren and Lotus in an uncanny way. His sensories all share the similiar looks as him, albeit with a minor differences. He often appears wearing long black tattered robes, though has been seen in various attires throughout the series.

Mercurius strives to achieve the unknown, not because he wants to learn more, but because he is hopelessly bored. He naturally possesses a relaxed, calm and manipulative demeanor, something that infuriates virtually everyone that he come into contact with. He is also philosophical and poetic and has a tendency of speaking for long periods of time.

(Source: Shinza Bansho Wiki)

An ominous magician and alchemist who created Ewigkeit and established the Obsidian Round Table. He was the one responsible for turning the LDO from a clique of elite army officers merely dabbling in the occult into a den of genuine demons. Not only is Mercurius the one sworn friend of the Table's leader, he also stands as the only being capable of matching his sublime prowess.

Although his position could be considered that of a mentor and a father, the other LDO members—with the exception of their master—shun him as a hateful taboo. His whereabouts have remained a mystery for the past six decades.

(Source: VNDB)