Dualism is a term introduced into modern theology by the Englishman, Thomas Hyde, in 1700, and was first used to describe sthe fundamental principle of Persian Zoroastrism, namely the independent existence of good and evil. Ormazd the good god and Ahriman the evil god in the theology of the Persians represent an absolute dualism. For them Ahriman, corresponding to Satan of Judaism and Christianity, is entirely independent of the creator god. Good and evil, God and the Devil, are primeval supreme powers. Now I wish to trace the history of Satan or the Devil in Christianity back through Judaism, Hebrew, and Babylonian religion to its origin among the Sumerians. I shall endeavour to prove this Persian dualism, which admits that God did not create the Devil, to be totally foreign to Sumerian, Babylonian, and Hebrew speculation; and I shall then briefly examine the evidence on which modern scholars admit dualism to have been held by the Jews of the Apocalyptic period and by early Christianity as set forth in the New Testament. It is my conviction that Persian religion never had any influence upon Judaism or early Christianity. Satan, the Devil (diabolus), is traceable directly to Babylonian theology; there he is the creation of the gods.