Revelation describes a heavenly battle in which “the great dragon was cast out, that ancient serpent, called the devil and Satan” (12:9). Satan being called a “serpent” (ophis; ὄφις) might remind us of the creature who deceives Adam and Eve (see Gen 3:1-6, 13). However, while the Greek Septuagint also calls the serpent of the Garden an ophis (Gen 3:1 LXX), the writer of Revelation is not referring to the snake we meet in Genesis.
We know that Revelation is not recalling the snake in Eden because the source of John’s language isn’t Genesis, it’s Isaiah. Along with calling the devil a “serpent” (ophis; ὄφις), Revelation first describes Satan as a “dragon” (drakon; δράκων). The only other verse in Scripture that we see a creature who is called both a “dragon” and a “serpent” is in Isaiah’s description of the primordial sea-monster, Leviathan. According to the Greek translation of the Hebrew Bible, the prophet states, “In that day God shall bring a holy and great and strong sword against the dragon (drakon; δράκων), the serpent (ophis; ὄφις) that flees, upon the dragon (drakon; δράκων), the twisting serpent (ophis; ὄφις): [God] shall destroy the dragon (drakon; δράκων)” (Isa 27:1 LXX). Since Isaiah repeats the words “dragon” and “serpent” several times in this verse, we can be confident that this is the very verse to which John refers in Revelation.
According to the original Hebrew text of Isaiah 27:1, the dragon that God will destroy at the end of days is called “Leviathan”: “In that day the Lord, with his heavy and great and strong sword, will punish Leviathan (livyatan; לויתן) the fleeing serpent (nachash; נחשׁ), Leviathan the twisting serpent (livyatan nachash ‘aqalaton; לויתן נחשׁ עקלתון), and he will slay the dragon (tannin; תנין) that is in the sea.” Elsewhere, the Bible refers to Leviathan as a great chaos monster of the sea that God defeats at the creation of the world (e.g., Ps 74:12-14). It is this ancient chaos creature that John calls “the devil and Satan” in Rev 12:9, rather than the snake in the Garden of Eden. The dragon of Revelation is a primal monster that represents the forces of chaos and disorder. Thankfully, in the end, God’s peace will prevail; Paul declares that “the God of peace (eirene; εἰρήνη) will soon crush Satan underneath your feet” (Rom 16:20). While Satan hopes that chaos will shatter, God works to achieve shalom.