The serpent in Eden was Satan, shown with horns and a pitchfork

Genesis 3:1 introduces the character as simply "the serpent," described as "more crafty than any other beast of the field that the LORD God had made": a wild animal, distinguished from the rest by cunning, with no cosmic identity attached in the passage itself. The identification with a fallen heavenly being develops later, gaining ground across Second Temple Jewish literature (the centuries between the Old and New Testaments), and finally becomes explicit in the New Testament's last book: "the great dragon was thrown down, that ancient serpent, who is called the devil and Satan" (Revelation 12:9).

The horns, red skin, cloven hooves, and pitchfork are a separate, much later layer: medieval and early-modern European art, which borrowed visual elements from depictions of the Greek god Pan (the horns and goat legs) and generic demonic iconography to give an abstract spiritual enemy a memorable face. None of it originates in, or is implied by, the Genesis text.

Michael Heiser's The Unseen Realm argues the plain "just a talking animal" reading undersells what the Hebrew itself is doing. The word nachash is genuinely ambiguous in the unvocalized consonant text: read as a noun it's "serpent," but the same root letters can form nochesh, "diviner," someone who communicates supernatural information, which fits the scene, since the nachash is doing exactly that to Eve. Heiser also connects the word's adjectival sense to nechosheth, "bronze" or "shining," tying the figure to other "shining one" language elsewhere in the Old Testament. On this reading, the text is already signaling something more than an ordinary animal from its very first verse, not by naming it Satan, but by choosing a word with that supernatural double meaning built in. That's a real scholarly argument, not settled consensus, and it still isn't the same claim as "Genesis 3 says this is Satan."