Satan is the head of the demons and led their rebellion against God; he now leads them in propagating evil in the world.
According to Scripture, Satan was a particularly powerful and high-ranking angel who led one third of the angelic host to rebel against God (Eph 2:2; Rev 12:1–12). Satan is a Hebrew word that means “adversary” (שָׂטָן). Scripture also refers to Satan as “the devil” (Matt 4:1, 5; Lk 4:2, 3; Eph 6:11), “the serpent” (Gen 3:1; 2 Cor 11:3; Rev 20:2), “the great dragon” (Rev 12:9; cf Rev 20:2), “the prince of the power of the air” (Eph 2:2), “the god of this age” (2 Cor 4:4), “the evil one” (Matt 13:19, 38; Jn 17:15; Eph 6:16), “the prince of demons” (Matt 9:34; 12:24; Mk 3:22; Lk 11:15), “the accuser” (Rev 12:10), and “the tempter” (Matt 4:3; 1 Thess 3:5). Like the other angels and demons, Satan is an invisible being who is highly intelligent and very powerful.
Satan was responsible for tempting Eve in the garden and leading humanity’s first parents into sin. Though Genesis never explicitly identifies the serpent as Satan, later Scripture identifies the “ancient serpent” as “Satan” (Rev 12:9; 20:2). Since his initial rebellion, Satan has continued to work against God’s righteous and saving purposes in the world. He actively opposes the propagation of the gospel by blinding unbelievers to its truth (2 Cor 4:4), persecuting the church (2 Cor 12:7; 1 Thess 2:17–18; Rev 2:10), and promoting false doctrine (Jn 8:44; cf 1 Tim 4:1). Satan actively seeks to incite Christians to fall into sin and is constantly attempting to ensnare them in unrighteousness (2 Cor 11:3). Satan is also an accuser, calling the faith of Christians into question before God and accusing them of sin (Job 1:9–11; Rev 12:10).
As a created being, Satan, though powerful, is not equal with God. Instead, like the other demons, he is wholly subject to God’s sovereign will (Job 1:6–12; 2:1–10).-Emadi, S. (2018). Satan. In M. Ward, J. Parks, B. Ellis, & T. Hains (Eds.), Lexham Survey of Theology. Lexham Press.
Any Bible dictionary will provide the above, what follows is the rest of the story they do not report.
Satan is more powerful than the Archangel Michael (Dan. 10:13; Jude 1:9), he is called the “anointed cherub” making him “Arch-cherub” among the Cherubim which is the highest order of created beings above seraphim and angels. While the other cherubim carried the throne of God, Satan was its “covering roof” a “canopy over the Throne” (Ez. 28:14).
“Perfect” in his ways until iniquity was found in him, he became prideful about his own beauty (Ez. 28:15, 17; 1 Tim. 3:6) and his wisdom was corrupted (Ez. 28:17), desiring to be worshiped (Isa. 14:13-15; Lk. 4:6-8). Rather than glorify God for his perfections, he became vain in his reasoning.
Satan looked deep within himself and saw iniquity, he had selfish motives for serving God. Likely “Confirmation Bias” convinced him the same was true for everyone. Therefore, God made a terrible mistake believing sentient life would share life with Him in mutual “true love”. As God made a mistake, His own criteria disqualified from being God (Is. 41:21-24). Satan then “trafficked (Ez. 28:5) his argument angel to angel, eventually convincing a third of likeminded angels to join his rebellion (Rev. 12:4).
Satan thought Job would prove to the heavenly court: “God’s pronouncement Job is blameless and upright is an error, God made a mistaking believing Job does not have selfish motives causing his devotion to God:
6 Now there was a day when the sons of God came to present themselves before the LORD, and Satan also came among them.
7 And the LORD said to Satan, “From where do you come?” So Satan answered the LORD and said, “From going to and fro on the earth, and from walking back and forth on it.”
8 Then the LORD said to Satan, “Have you considered My servant Job, that there is none like him on the earth, a blameless and upright man, one who fears God and shuns evil?”
9 So Satan answered the LORD and said, “Does Job fear God for nothing?
10 “Have You not made a hedge around him, around his household, and around all that he has on every side? You have blessed the work of his hands, and his possessions have increased in the land.
11 “But now, stretch out Your hand and touch all that he has, and he will surely curse You to Your face!”
12 And the LORD said to Satan, “Behold, all that he has is in your power; only do not lay a hand on his person.” So Satan went out from the presence of the LORD. (Job 1:6-12 NKJ)
Satan lost his case, God was right about Job. But Satan’s main argument, “there is a selfish motive for every act of devotion to God” still seemed incontrovertible to a third of heavens angels (Rev. 12:3-4) No doubt “confirmation bias” contributed to their error, they projected their own selfish motives onto others.
What incontrovertible proof “unselfish love” exists would convince the heavenly court? The incarnation of Christ.
Jesus proved unselfish love exists when He made Himself of no reputation leaving all the privileges and prerogatives of Godhood because He loved the Father more than life itself and loved man with true unselfish love.
4 Let each of you look out not only for his own interests, but also for the interests of others.
5 Let this mind be in you which was also in Christ Jesus,
6 who, being in the form of God, did not consider it robbery to be equal with God,7 but made Himself of no reputation, taking the form of a bondservant, and coming in the likeness of men.
8 And being found in appearance as a man, He humbled Himself and became obedient to the point of death, even the death of the cross.
9 Therefore God also has highly exalted Him and given Him the name which is above every name,
10 that at the name of Jesus every knee should bow, of those in heaven, and of those on earth, and of those under the earth,
11 and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father. Phil. 2:4-11 NKJ)
The Father proved unselfish love exists, when He gave His only begotten Son the “apple of His eye” so all who believe in Him shall not perish.
“For God so loved the world that He gave His only begotten Son, (Jn. 3:16 NKJ)
Therefore, both the Father and Son incontrovertibly establish unselfish love exists:
It is written:
By the mouth of two or three witnesses the matter shall be established. (Deut. 19:15 NKJ)
The incarnation of Christ so irrefutably proved Satan wrong demons cannot say “Jesus Christ came in the flesh”, they choke on the words as the terror of the LORD overwhelms all rational thought.
2 By this you know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is of God,
3 and every spirit that does not confess that Jesus Christ has come in the flesh is not of God. And this is the spirit of the Antichrist, which you have heard was coming, and is now already in the world. (1 Jn. 4:2-3 NKJ)
That is the origin of Satan and his fallen angels. They “bet the farm” God would disqualify Himself from being God once Satan proved He made a great mistake creating intelligent free willed life to dwell with, in mutual “true love”:
13 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;
14 I will ascend above the heights of the clouds, I will be like the Most High.’
15 Yet you shall be brought down to Sheol, To the lowest depths of the Pit.
16 “Those who see you will gaze at you, And consider you, saying:`Is this the man who made the earth tremble, Who shook kingdoms,
17 Who made the world as a wilderness And destroyed its cities, Who did not open the house of his prisoners?’
18 “All the kings of the nations, All of them, sleep in glory, Everyone in his own house;
19 But you are cast out of your grave Like an abominable branch, Like the garment of those who are slain, Thrust through with a sword, Who go down to the stones of the pit, Like a corpse trodden underfoot.
20 You will not be joined with them in burial, Because you have destroyed your land And slain your people. The brood of evildoers shall never be named. (Isa. 14:13-20 NKJ)