Now the serpent was the most cunning of all the wild animals that the Lord God had made. He said to the woman, “Did God really say, ‘You can’t eat from any tree in the garden’?” -Genesis 3:1
The serpent is the one who caused mankind to fall into sin by deception and brought about their death, physical and spiritual—separation from God.
So the great dragon was thrown out—the ancient serpent, who is called the Devil and Satan, the one who deceives the whole world. He was thrown to earth, and his angels with him. -Revelation 12:9
The serpent of Genesis is none other than Satan himself. The phrase “the ancient serpent” reveals that Satan’s fall happened before the first humans were created.
You are of your father the Devil, and you want to carry out your father’s desires. He was a murderer from the beginning and has not stood in the truth, because there is no truth in him. When he tells a lie, he speaks from his own nature, because he is a liar and the father of liars. -John 8:44
Jesus was speaking to the Jews who wanted Him dead—giving a comparison of their desires to that of Satan’s because he was the first murderer, referring to the serpent’s deception that ended up destroying Adam and Eve’s relationship with the LORD—bringing upon their death. And was now behind these men—stirring them to murder Jesus.
The gospel of Jesus Christ is where you will find the Truth.
Any other source that reveals the nature of God other than the Scriptures, you will find the teachings of Satan which will bring you false doctrine, and is also known as doctrines of demons (1 Timothy 4:1-2).
Who is the serpent? Satan. The first murderer and the father of lies.