Name: Sir Conrart/Conrad Weller

Aliases:
The Lion of Lütenberg
The Patriot of Lütenberg
Commander
Captain (Taichou)- by Josak
Lord Weller (Weller-kyo)- by people in general, including Wolfram
Conrad - by Yuuri (who claims it is easier to pronounce than his given name, Conrart) Later on in the series, Wolfram and Gwendal also call him this.
Man-Who-Named-Me/ (Nazukeoya)- by Yuuri. This is similar to Godfather.
Little Big Brother (Chiisai aniue)- young Wolfram
Sir Weller - by Suzanna Julia von Wincott

Race: Half human, half Mazoku
Gender: Male
Birthday: Summer
Age: 96 (Appears 20+)
Hair Color: Light Brown
Eye Color: Light Brown w/ silver specks
Status: Second son of the previous Maoh, Commander of Security. He oversees Yuuri's Safety.
Clothing: 1914 German Infantry Uniform

Conrad is a swordsman ("the best swordsman in Shin Makoku" - according to Wolfram) who looks after Yuuri. He possesses no maryoku (demonic magic) due to his mixed heritage of human and mazoku. His given name is Conrart; Yuuri nicknames him "Conrad," which is "closer to English" and easier to pronounce with a Japanese tongue. Conrad is the second child of the previous Maou, Cecilie von Spitzweig. His father was human (also considered the greatest swordsman in the Demon Kingdom; Dan Hiri Weller). His ancestor, Lawrence Weller, fought alongside the Original King during the war against Soushu. As Conrad's father was not a Mazoku noble, he doesn't have "von" in his name.

On his 16th birthday, he decided to live as a Mazoku instead of a human. He fought on the front lines for the Mazoku during a war against the humans. He and Yozak are the only two survivors of the Battle of Lütenburg, and at the request of Julia von Wincott, he was also put in charge of the soul that was to be the new Maoh. He transported it safely to Earth so that it could be born.

Furthermore, he was the one who was the inspiration for Yuuri's name. He stated that "Where I come from, the month of July is called Yuuri", which made Yuuri's mother name him 'Yuuri' because he was born in July. For this reason, Yuuri dubs him 'Nazukeoya', which is a person who names someone (Conrad is also known as Yuuri's Godfather by his mother). Cecilie named the blue flowers she grew "Conrad Stands Upon Earth".

When Yuuri first came to Shin Makoku, Conrad was the one to find him (after some humans and Adelbert) and bring him safely to the castle. He acts as Yuuri's bodyguard and vows to protect Yuri with his life. He was described by Yuri as almost perfect with fine looks and a mild demeanor but he makes the worst jokes. Typically, he could be found with an unassuming smile on his face, and persists in calling Yuuri 'Heika (Your Majesty)' except in dire situations, and when Yuuri scolds him for it.



He was also very close to Suzanna Julia von Wincott, whose soul now resides inside Yuuri.

Source: wikipedia.org