In Christianity, the Devil is the personification of evil who rebelled against God in an attempt to become equal to God himself. He is depicted as a fallen angel, who was expelled from Heaven at the beginning of time, before God created the material world, and is in constant opposition to God. The devil is identified with several figures in the Bible including the serpent in the Garden of Eden, Lucifer, Satan, the tempter of the Gospels, Leviathan, and the dragon in the Book of Revelation.

Early scholars discussed the role of the devil. Scholars influenced by neoplatonic cosmology, like Origen and Pseudo-Dionysius, portrayed the devil as representing deficiency and emptiness, the entity most remote from the divine. According to Augustine of Hippo, the realm of the devil is not nothingness, but an inferior realm standing in opposition to God. The standard Medieval depiction of the devil goes back to Gregory the Great. He integrated the devil, as the first creation of God, into the Christian angelic hierarchy as the highest of the angels (either a cherub or a seraph) who fell far, into the depths of hell, and became the leader of demons.

Since the early Reformation period, the devil has been imagined as an increasingly powerful entity, with not only a lack of goodness but also a conscious will against God, his word, and his creation. Simultaneously, some reformists have interpreted the devil as a mere metaphor for humans' inclination to sin - thereby downgrading his importance. While the devil has played no significant role for most scholars in the Modern Era, he has become important again in contemporary Christianity.

At various times in history, certain heretical sects such as the Cathars and the Bogomils, as well as theologians like Marcion and Valentinus, have believed that the devil was involved in creation. Today these views are not part of mainstream Christianity.