The Western religions of Judaism, Christianity, and Islam have all accepted the belief that there is, between God and mankind, a class of intermediary beings called angels. The word angel comes from the Greek word angelos, meaning "messenger." Angels are considered to be bodiless minds or spirits who perform various services for God or for people on God's behalf. Angels are good spirits. They have their counterpart in demons, or evil spirits.

Angels are frequently mentioned in the Bible, mostly in the role of messengers from God to mankind. Their appearances on Earth seem to have been in human form. In the Old Testament books of Job, Ezekiel, and Daniel, as well as in the Apocryphal book of Tobit, angels play significant roles. In the Book of Job the leading demon, Satan, is also introduced. But it is not until the New Testament that Satan is portrayed, under the name Lucifer, as the first of the fallen angels--the angels that rebelled against God.

 In the New Testament, angels are present at all the important events in the life of Jesus, from his birth to the Resurrection. In the very dramatic Book of Revelation, angels are portrayed as the agents of God in bringing judgment upon the world. Other New Testament writers also speak of angels. St. Paul especially takes note of them by assigning them ranks. He lists seven groups: angels, archangels, principalities, powers, virtues, dominions, and thrones. The Old Testament had spoken of only two orders: cherubim and seraphim.

Early Christianity accepted all nine ranks and in the course of time developed extensive doctrines about both angels and demons. The latter were conceived of as Satan's legions, sent out to lure mankind away from belief in God. Angels and demons play similar roles in Islam and are often mentioned in its holy book, the Koran.

In John Milton's long poem 'Paradise Lost' (1667), Satan himself is a main character; and the angels Raphael, Gabriel, and Michael play prominent roles. In Dante's 'Divine Comedy' (1321?) angels appear as both messengers and guardians, and Satan is vividly portrayed frozen in a block of ice.