The Story of Satan:
Isaiah 14

Introduction
Believe it or not, Satan was an angel of God.  Satan was the most beautiful angel in heaven, named Lucifer.

Lucifer in Heaven
Lucifer was prideful and jealous of God.  He wanted to be worshiped, too.  Lucifer was cast out of heaven like a bolt of lightning and was stripped of his beauty, name, and rights to heaven.  He was joined by several other angels, who later became demons.

Lucifer / Satan on Earth and in Hell
Now Lucifer's motive was to oppose the mighty plan of God.  He tempts you, me, and he even tempted Jesus (Matthew 4:1-11).  All that Satan wants to do is harm you and flip you to his side.

Defending Against Satan
When you are saved, you don't have to worry about Satan.  Once you are saved, you are going to heaven, but now you can live for God, not Satan.  Yes, Satan will still tempt you, but he will no longer be able to hurt you.  There will be angels protecting you at all times from Satan's evil demons.  They will battle for you, but you won't even realize that they are there.

That is God protecting you.  Yes, there will be a battle against Satan, his demons, and his new human allies, but God will win.  God always wins.