The Belial Clan is one of the remaining 32 Devil Clans of the 72 Pillars and one of the lowest-ranking Devil families; among the poor aristocracy. The current Lord is Diehauser's father who became the Lord again due to his son being stripped of the rank.
The clan that produced the strongest player in the Rating Game, members of the Belial clan are noted for their signature power called Worthless. The ancestors from the previous few generations were unknown people who made constant errors in the Great War of the Three Factions as well as during the Devil Civil War of the old government, causing the strength and authority of the clan to continuously decline. The Belial family faced financial difficulties but managed to just scrape by until Diehauser's success in the Rating Games finally solved this difficulty as his continuous victories in Rating Games allowed him to promote products made in the Belial domain and increase the wealth of the Belial family.
Members of the Belial clan could be compared to the Gremory clan for their affection to others around them, though less immense. The members take good care of their family and the citizens within the Belial's territory, despite their standard of living being in a poor state. The territory of the Belial clan is not particularly prosperous although the citizens do not face difficult lives. Tax received from the citizens is quite low: being one of the reasons for the clan's low ranking, which caused them to be ridiculed by some of the elite.
Members of the clan possess the ability known as Worthless, which allows them to nullify both offensive and defensive abilities, so long as they understand the properties of the ability.
The only known members of the clan are Diehauser, Cleria, Lord Belial, Calfa Belial, and Diehauser's uncle and grandfather.
|Diehauser's Grandfather||A former Head of the House of Belial, father of Lord Belial and an unnamed son, father-in-law of Calfa Belial, grandfather of Diehauser and Cleria Belial. Not much is known about him.||High-Class Devil||Pure-Blood Devil||Alive|
|Lord Belial||The current Head of the House of Belial, husband of Calfa Belial, brother of an unnamed brother, father of Diehauser Belial and uncle of Cleria Belial.||High-Class Devil||Pure-Blood Devil||Alive|
|Calfa Belial||The current Lady of the House of Belial, wife of Lord Belial, mother of Diehauser Belial, sister-in-law of an unnamed brother-in-law, and aunt-in-law of Cleria Belial. Not much is known about her other than she disagreed with her son partaking in the Rating Games, due to her worry of seeing him get hurt.||High-Class Devil||Pure-Blood Devil||Alive|
|Diehauser's Uncle||The son of an unnamed father, brother of Lord Belial, brother-in-law of Calfa Belial, father of Cleria Belial, and uncle of Diehauser Belial. Not much is known about him.||High-Class Devil||Pure-Blood Devil||Alive|
|Diehauser Belial||The former Head of the House of Belial, son of Lord Belial and Calfa Belial, grandson of an unnamed grandfather, nephew of an unnamed uncle, and cousin of Cleria Belial. Diehauser lost his right to be the Head of the clan due to his involvement with Rizevim.||Ultimate-Class Devil||Pure-Blood Devil||Alive|
|Cleria Belial||The daughter of an unnamed father, granddaughter of an unnamed grandfather, niece of Lord Belial, niece-in-law of Calfa Belial, and cousin of Diehauser Belial. She was the High-Class Devil who ruled Kuoh Town before Rias Gremory.||High-Class Devil||Pure-Blood Devil||Deceased|
- In Volume 18, it was mentioned that Cleria Belial was from a Branch Family in the House of Belial.
- Belial is a proper noun for the Devil or Satan in Jewish and Christian texts.
- 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.
- 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.
- In demonology, Belial is the chief demon of vanity, which is said to be a sin and sometimes included in the list of "seven deadly sins".