Where did the devil come from?
The devil was once a high-ranking angel who was originally perfect in all his ways. At some point in the past, he was overcome with pride and instigated a large rebellion against God. The Lord reacted by kicking the devil out of Heaven. It was such an uneven match that Jesus described Satan as falling from heaven as lightning (Luke 10:18).
"How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations! For thou hast said in thine heart, I will ascend into heaven, 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: I will ascend above the heights of the clouds; I will be like the most High" (Isaiah 14:12-14).
The devil and his followers will eventually spend eternity in hell. The lake of fire was originally designed for them alone. It wasn't until later when Adam and Eve disobeyed God that mankind became linked to sharing the devil's fate.
"And there was war in heaven, Michael and his angels waging war with the dragon. The dragon and his angels waged war, and they were not strong enough, and there was no longer a place found for them in heaven. And the great dragon was thrown down, the serpent of old who is called the devil and Satan, who deceives the whole world; he was thrown down to the earth, and his angels were thrown down with him" (Rev. 12:7-9, NAS '95).
"Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels" (Mat. 25:41 KJV).
