Asura

The first-generation Kishin and one of the Great Old Ones whose affinity to madness resides in fear. He formerly served as one of the Warlords of the Eight Reaper Legions, being its most powerful member until he betrayed the group and became a Kishin, killing innocents to gain power through their souls and even consuming his own demon weapon partner, as well as two other Great Old Ones. After his betrayal he was sealed away by Death, and remained sealed until his revival by Medusa's Faction.

Manga:

He is later revealed to be Death's eldest son and the older brother of Death the Kid, specifically created as a fragment containing all of Death's fear in order for Death to become the God of Absolute Order.

After Asura's battle with Maka, Black Star and Death the Kid, Crona seals both Asura and themselves inside the moon to keep his madness locked away from the world. Asura gleefully asserts that this method will not last, and that one day he will return to terrorize the world again.