From my understanding on Satan:
Satan was God's firstborn son, the first Cherub. Satan is the most beautiful being traditionally, hence His inherent ability to deceive. The Great Deceiver, Father of Lies, the Great Prosecutor. His job is to decide whether you go to Hell or go to St. Peter's gates again out of purgatory/layers of Perdition. There are 666 layers of Perdition; when you die you go to the first Great Exam; you awaken where you died sinning the way you did that caused you to die until you fully repent of that. Your secondary sin is your second Perdition until you repent, and so-on until you repent of all 666 original sins (7 deadly sins is a lie)