9. Who is Satan?

Satan is the being of evil who is antagonistic in deeds and design to God. Satan (or Lucifer as he was then called) was created a covering Cherub. Evil was found in him when he became lifted in pride and decided he wanted to be like the Most High. Satan and the angels that decided with him were thrown out of heaven.

– Isaiah 14:12
12. How are thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!
13. For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north:
14. I will ascend above the heights of the clouds; I will be like the Most High.
15. Yet thou shalt be brought down to hell, to the sides of the pit.
16. They that see thee shall narrowly look upon thee, and consider thee, saying, Is this the man that made the earth to tremble, that did shake kingdoms.
17. That made the world as a wilderness, and destroyed the cities thereof; that opened not he house of his prisoners?

See also, Ezekiel 28:12-19, Jude 1:6