The original name given to the devil was Lucifer (Isaiah 14:12), which means "son of the morning." He was blessed with unmatched wisdom, beauty and musical talents (Ezekiel 28:12 - 13, 15). God himself declared, "you seal up the measure of perfection" (Ezekiel 28:12, HBFV throughout). Lucifer was the greatest being the Eternal could make from scratch (verse 15).
Lucifer, before becoming the devil, was blessed with the responsibility of serving God at his throne (Ezekiel 28:14). After faithfully performing this task he was rewarded with a new job. He was given the first and only known angelic promotion to his own throne where he would supervise, on earth, one third of all the angels.
For you (Lucifer) have said in your heart, 'I will ascend into the heavens, I WILL EXALT MY THRONE above the stars of God; I will also sit upon the mount of the congregation, in the sides of the north.' (Isaiah 14:13, HBFV, see also John 12:31, Revelation 12:3 - 4).
It was during his supervisory responsibility on earth that he became the devil (Isaiah 14:13 - 14, Ezekiel 28:15).
God can bless any individual he brings into existence with a plethora of gifts, talents and powers. There is one critical attribute, however, he could not give Lucifer to insure he would never reject his ways and turn himself into the devil. He could not give him, when created, the same unchangeable righteous character he possessed.
The attainment of holy character that will never change requires choices made over time (Ephesians 4:13, Philippians 3:12, 2Timothy 3:17, Hebrews 13:21). The intensity or zealousness of a being's thoughts and behavior also plays a vital role (Romans 12:11, James 5:16, 1Peter 4:8).
Christians are promised that if they lead a faithful life of overcoming and obedience they will be sealed sinless and holy forever (1Corinthians 15:52 - 54, Romans 8:21, Revelation 21:7).
Rejecting His Reward
Lucifer was rewarded with more responsibilities by God, and a far more active role in serving others, as an opportunity to seal his character in righteousness. He choose, however, to believe his new authority, coupled with his unique attributes (e.g. beauty), made him better than everyone else including his Creator! This led to him becoming vain (Ezekiel 28:17) and turning into the devil.
It is possible that Lucifer turned himself into the devil within a relatively short period. His shift from the way of God to a vain and violent (hate intense) lifestyle, coupled with the frequency and intensity of his evil thoughts (referred to as "the multitude of your merchandise," see Ezekiel 28:16 - 18) may have led to his character quickly and permanently setting to evil.
God did not create Satan the devil but he did create Lucifer. It was Lucifer who turned himself, through vanity and lust, in the Eternal's great adversary. He then promulgated, to those angels he supervised, the same deceptions and lies he believed. Both Lucifer and the angelic host under him turned themselves into demons and the enemies of all righteousness.