Asura is the first generation Kishin and Great Old One whose affinity to Madness resides in the Madness of Fear. Asura is the main antagonist as well as the most powerful, evil, and dangerous villain of Soul Eater.

Asura served under Lord Death as a member of the Eight Powerful Warriors. Asura was the most valued member of the group, said to be the strongest and most feared among all its members. However, Asura was a very fearful person, nearly always frightened by something or seen mumbling to himself eerily. The Weapon Vajra took it upon himself to partner with Asura in an effort to relieve him of some of his fears, but only end up being eaten by Asura who after that started to eat humans souls and turned into a Kishin and started to spread madness and chaos across the world. Lord Death was forced to hunt his own son, skin him alive and use that skin to seal him and his madness.

(Source: Villains Wikia)