In my recent novel, Halo of the Damned, I used research about an ancient Middle Eastern religion, Yezidism. The Yezidis originated from northern Iraq and spread throughout the Kurdish community, eventually making its way into part of Europe.
Yezidis worship angels, especially Malak Tawas who many believe to be Satan. The peacock symbolizes this angel. Malak Tawas' story in the Koran matches the stories in the Bible and Old Testament about a rebellious angel who wages war with a third of all of God’s angels against God. Once defeated, God sends all of them to Hell and denies them mercy.
Yezidis believe God created Malak first, before all other angels, in His image, therefore he is also God. They also believe the world was first created as a pearl. Their holy books are Black Book and Book of Revelation. Their afterlife ideas are vague, but lean towards reincarnation. I found the religion fascinating and used it for my plot.