Diehauser Belial

Diehauser Belial is the current head of the Belial Family and the Rating Game champion, ranking number one.

Appearance
Diehauser is described as a man with a graceful face who has grey hair and grey eyes.

Personality
Diehauser is shown to be a polite man and respects his opponents and the young Devils who are rising regardless of their background, unlike most Devils who take importance in things such as pure bloods and demonic powers.

History
Diehauser has been dominating the Rating Game for a very long time, being undefeated since appearing, and is popularly known as "The Emperor" (皇帝 Kōtei) to everyone in the Underworld. He also had a close relationship with his cousin Cleria Belial whom he views as a little sister and was surprised at her unexplained death which he has continued to investigate on ever since.

The Heroic Oppai Dragon
He served as Sairaorg's mentor throughout the Young Devils Gathering and was one of the spectators at Rias and Sairaorg's Rating Game, complimenting Issei and Sairaorg for their magnificent fight during the news conference after their battle.

In Volume 12, Diehauser and his peerage went to fight against the Jabberwocky created by Leonardo's Annihilation Maker but they were only capable of stalling it. He later leads an alliance army from various factions to battle one of the Bandersnatch, being the first group to defeat the monsters.

The Legend of Oppai Dragon and his Lively Companions
In Volume 17, Diehauser was present at the opening of Auros Academy. He came to encourage the Gremory, Sitri and Bael Groups. At the end of Volume 17, Diehauser was revealed to be a traitor to the Underworld, stating that he only wanted to fulfill the wishes of his "true king", Rizevim Livan Lucifer. He joined the Khaos Brigade to investigate an incident that had occurred in Rias' territory (which had previously belonged to his relative) which, according to him, involved Touji Shidou, Heaven, and the Underworld.

In Volume 19, he fights against Riser Phenex in a rating game, in which he uses his powers to disable both Riser and Ravel Phenex's regenerative abilities, as well as the retiring system, which draws the attention of Tiamat.

In Volume 20, just before Issei and Asia arrived to fight him and Rizevim on the top floor, Diehauser used Agreas' broadcast system to expose the secret of the King Piece used by several top rankers and the Old Devil's corrupt control of the Rating Games.

When confronted by Issei, Diehauser told him that he only told the public the truth, and revealed his cooperation with the Qlippoth. Rizevim arrived and, after a short exchange of words and Vali's arrival, Diehauser commenced fighting Issei while Rizevim fought Vali. Diehauser easily overwhelmed Issei, making use of his house's Worthlessness ability, while also critiquing Issei's form. Diehauser then proceed to force Issei to drink dragon's blood at Rizevim's command. Although he continued his fight with Issei, but he lost his will to fight after seeing the amount of damage Issei had sustained. Later, when Rizevim's Phoenix Tears did not work, Diehauser revealed that he had used his clan's special trait to nullify them. Upon Rizevim's defeat, Diehauser told Issei to cast judgment on him, but Issei's mother slapped him, saying she would not let Issei do that. Finally, he asked Issei if he had seen Cleria in heaven. Issei replied that he had and that she had a kind face. With tears in his eyes, Diehauser declared that Issei had defeated him.

Red Dragon Emperor of the Blazing Truth × White Dragon Emperor of the Morning Star: The True Dragon(s) of the Kuoh Academy
In Volume 22, while he didn't attend to the opening ceremony of the Azazel Cup, his queen attended the ceremony in his stead.

Powers & Abilities
Immense Demonic Power: As the Champion of the Rating Game, Diehauser is a immensely powerful Devil. In fact, his power rivals that of a Satan-class Devil. Diehauser, unlike many of the top-ranked Devils, got to the top on his natural abilities and talent, without using a King piece to strengthen himself. Yuuto mentioned that the top 5 champions of the Rating Game are considered to be unmovable from their positions and that they are the Ultimate-Class Devils of Ultimate-Class Devils which is further testament to Diehauser's power. Bedeze Abaddon the third ranker of the Rating Games called Diehauser a monster with absolute power and the Rookies Four are far inferior to Diehauser.
 * Worthlessness: As a member of the House of Belial, Diehauser is able to nullify the abilities of people or objects. However, he must understand the properties of the ability in order to render it "worthless." He can also apply Worthlessness in his demonic power attacks, inflicting damage while nullifying any defensive abilities his opponent may possess as shown in his rating game with Riser when he attack Ravel which nullified her regeneration abilities.

Immense Strength: Diehauser displays immense strength, easily able to physically overpower Issei in his Balance Breaker state and force him to drink dragon's blood.

Immense Durability: Diehauser has immense durability. During his fight with Issei, Issei commented that even if he were to use the Longinus Smasher, Diehauser would have still be able to stand up.

Master Hand to Hand Combatant: Diehauser has tremendous mastery in hand to hand combat. Combined with his Worthlessness ability, Diehauser was able to block all of Issei's attacks, while completely remaining on the defensive.

Trivia

 * In demonology, Belial is listed by Abramelin as one of the Four Crown Princes of Hell (with Lucifer, Satan and Leviathan) and a demon in the Bible. In the Ars Goetia, he is said to be a mighty and a powerful king, ruling over 50 legions of demons made after Lucifer. From other sources, Belial is usually listed as a king, a prince, or a lesser prince of Hell.
 * The term belial (בְלִיַּעַל bĕli-yaal) is a Hebrew adjective meaning "worthless", which serves as the namesake of Worthlessness, the symbolic power of the Belial Clan.