Genesis 3 introduces the serpent simply as the most cunning of the creatures, and the text does not, at that point, name him. He works by a question that reframes God's generosity as restriction ('Did God really say…?'), then a flat denial of God's warning, then the promise that the forbidden thing will make the creature like God. It is the template of every temptation since: doubt God's word, deny its consequences, and offer autonomy as the prize. Yet in the same chapter comes the first promise of the gospel — Genesis 3:15, the 'protoevangelium' — that the seed of the woman will crush the serpent's head, even as the serpent strikes his heel.
Scripture's last book reaches back and names him: 'the great dragon… that ancient serpent, who is called the devil and Satan, the deceiver of the whole world' (Revelation 12:9; cf. 20:2). The canon is deliberately bracketed — a serpent in the garden at the beginning, the same serpent as a bound dragon at the end. Whether the Eden serpent was 'Satan' is something Genesis leaves implicit and the New Testament makes explicit; Theologos follows the canon's own identification while noting that it is the whole-Bible reading, not a detail stated in Genesis 3 itself.
Between the garden and the consummation stands the cross. Paul tells the Romans, 'The God of peace will soon crush Satan under your feet' (Romans 16:20), consciously echoing Genesis 3:15 — the promise of the crushed head is being kept in the life of the church. The serpent's oldest weapon is still the lie (John 8:44 calls him 'a liar and the father of lies'), and his oldest tactic still works by 'cunning' (2 Corinthians 11:3). But his head is already crushed; what remains is the mopping up of a defeated foe.
The promise of Genesis 3:15 — the seed of the woman crushing the serpent's head — was kept at the cross and the empty tomb; the ancient serpent strikes only a heel, and is himself undone (Hebrews 2:14; Revelation 12:11).