Arioch is a Lord of Chaos in Michael Moorcock's Eternal Champion series. He is the patron god of Elric of Melnibone, and his kingdom.

Arioch is very intelligent and manipulative. He has taken a special interest in Elric , and constantly urges him toward serving chaos. He usually appears as beautiful androgynous man, naked and surrounded by fire. Sometimes, though, due to magical distortions, one may catch a glimpse of his true appearance, too horrible and deformed for words.

Arioch has been encountered by another Eternal Champion, Corum Jhaelen Irsei. Arioch was known here as the Knight of the Swords, one of three gods who ruled over Corum's world. The Knight of the Swords was the creator of the humans, or Mabden, as they were known in this world. When Corum first saw Arioch, he was a massive, filthy creature, with Mabden servants all over his body. Later, he appeared to Corum in the more familiar form of an attractive man.

Arioch is named after a legendary demon created during the era of demonology.