An angel is a supernatural being found in many religions. In Christianity, Judaism, Zoroastrianism and Islam, they typically act as messengers from God. Angelology is a branch of theology that deals with a hierarchical system of angels, messengers, celestial powers or emanations, and the study of these systems. It primarily relates to kaballistic Judaism and Christianity, where it is one of the ten major branches of theology, albeit a neglected one.
Many secular scholars believe that Judeo-Christianity owes a great debt to Zoroastrianism in regards to the introduction of angelology and demonology, as well as the fallen angel Satan as the ultimate agent of evil, comparing him to the evil spirit Ahriman. As the Iranian Avestan and Vedic traditions and also other branches of Indo-European mythologies show, the notion of demons had existed long before.