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 12:9 describes Satan as a “dragon” (drakon; δράκων) three times. The only other verse in all of Scripture that describes a creature as both a “dragon” and a “serpent” in this way is Isaiah 27:1, and the creature is the primordial sea-monster known as Leviathan. The Isaiah verse appears in the context of God’s eschatological battle against evil, which is the very same context that readers encounter in Revelation when Michael and his angels confront Satan (see Rev 12:7-9). According to the Greek translation of the Hebrew Bible, Isaiah 27:1 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).” Revelation 12:9 contains the same threefold repetition of “dragon” that appears in Isaiah 27:1, and both verses repeat the word alongside “serpent” in the context of divine battle. Therefore, we can be confident that Isaiah 27:1 is the verse to which Revelation refers in its description of heavenly war against Satan.
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 monster 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 Revelation 12:9, not the snake in the Garden of Eden. These different creatures populate the separate realms of land and sea: Leviathan swims in the sea (see Job 3:8; 41:1; Ps 104:26; cf. 4 Ezra 6:49-52) but the garden snake is an “animal of the field” (Gen 3:1) that eats the “dust” of the ground (3:14). Revelation rightly identifies Satan with Leviathan — both monstrous 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).