Who is Satan, who created him?

God did not create Satan as a devil.

Satan was an angel, he was one of the cherubim and having fallen down, he became a devil or a stubborn contestor of God.

God said about him: “You were the anointed cherub who covers” (Ez. 28:14, 16).
He said about his qualities: “You were the seal of perfection, full of wisdom and perfect in beauty I established you; you were on the holy mountain of God; you walked back and forth in the midst of fiery stones. You were perfect in your ways from the day you were created, till iniquity was found in you (Ezekiel 28: 12, 14-15). It is the tragedy of failure!

A fallen angel

Thus were his high rank and his glorious qualities, till he fell.
Satan, cherub angel, fell by means of pride.

The story of his fall is mentioned in the book of the prophet Isaiah.

The Scriptures say about him: “For you have said in your heart: “I will ascend into heaven, I will exalt my throne above the stars of God; I will also sit on the mount of the congregation on the farthest sides of the north; I will ascend above the heights of the clouds, I will be like the Most High” (Is. 14: 13-14). And it was said of him in the book of the 17 prophet Ezekiel: “Your heart was lifted up because of your beauty; you corrupted your wisdom for the sake of your splendor” (Ez. 28:17).
With the fall of Satan, he made many other angels fall with him.

These have become among his forces and hosts. They have become devils like him, opposing God. The Scriptures have surnamed them: “spiritual hosts of wickedness” (Eph. 6:12). Among them were “rulers and principalities”.

But the Scriptures did not mention that anyone of the rank of the thrones fell, because they symbolise the divine presence, nor from the rank of the seraphim, because they represent the praise of God and the divine love, from their name which means “the powerful with fire”, or “the flaming with love”.
With the fall of Satan, he lost his place in heaven and descended to earth.

The book of the Apocalypse says about that: “And war broke out in heaven: Michael and his angels fought with the dragon; and the dragon and his angels fought, but they did not prevail, nor was a place found for them in heaven any longer. So the great dragon was cast out that serpent of old, called the Devil and Satan, who deceives the whole world, he was cast to the earth, and his angels were cast out with him” (Apoc. 12: 7-9).

The archangel Michael confronted him with an army of righteous angels, and he conquered him, and threw him out of heaven, together with his wicked angels.
With the fall of these angels, who are souls, they were surnamed the “unclean spirits” (Matt. 10:1), or “the evil spirits” (Acts 19:12), and sometimes the “deceiving spirits” (1 Tim. 4:1).
Although the devils, with their fall, have lost their purity, nevertheless they have not lost their nature as angels with the strength which they possess.

The strength of the devil appeared for instance, in his test of the just Job. He was able to bring down fire from heaven, and it “burned up the sheep and the servants” (Job 1:16). He was able to raise up “a great wind” which “came from across the wilderness and struck the four corners of the house, and it fell on the young people,” and they were dead. (Job 1: 16,19).

The devil was able also to strike Job “with painful boils from the sole of his foot to the crown of his head. And he took for himself a potsherd with which to scrape himself” (Job 2; 7-8).
Likewise a devil withstood Gabriel twenty-one days, while he was going to deliver the prophet Daniel, and he delayed him till “Michael, one of the chief princes, came to help” him:” (Dan. 10:12-13).
The devils of the country of the Gadarenes (Legion) were able to enter the swine, and they drowned them into the sea” (Luke 8:33).

Likewise their strength appears in witchcraft, and their support of the sorcerers.
Satan works also in deceiving and cheating.
As the apostle saint Paul said: “for Satan himself transforms himself into an angel of light”: (2 Cor. 11:14).
He has in this domain numerous stories with the saints: for example, once he appeared to a father of the desert and said to him: “I am the archangel Gabriel, and I was sent to you“. Then the saint humbly replied to him: “May be you have been sent to another one and you have lost your way. As for me, I am a sinner and do not deserve that an angel appears to me“.

The Lord said about Satan that “he is a liar and the father of it” (John 8:44).

The devils have done many other actions, and they have killed many people. Therefore the Lord gave to his disciples “power over unclean spirits, to cast them out (Matt. 10:1). The Lord gave us, in spite of the strength of the devil, “the authority to trample on serpents and scorpions and over all the power of the enemy” (Luke 10:19).
In the book of the biography of saint Antonios (which was written by saint Athanassius), there is a long sermon which he said about the weakness of the devils.
The most dangerous action which Satan will do, is his support for the Anti-Christ who will cause the general “falling away” at the end of time.

That is about which the apostle saint Paul said: “The coming of the lawless one is according to the working of Satan; with all power, signs, and lying wonders, and with all unrighteous deception among those who perish”, “whom the Lord will consume with the breath of His mouth and destroy with the brightness of His coming” (2 Thess. 2: 8-10).
As to the end of Satan, it is “the lake of fire and brimstone”.
The book of the Apocalypse says about that: “The devil, who deceived them, was cast into the lake of fire and brimstone where the beast and the false prophet are. And they will be tormented day and night forever and ever” (Apocalypse 20:10).