What is the difference between Satan and Lucifer?
Are Lucifer and Satan the same entity?
According to theologists and learned occultists, both modern and ancient, the simple answer is no. Satan was created to test the integrity of man, to allow man to show his strength in the face of adversity and love for God. Lucifer was a Fallen Archangel, His sin, pride.
The confusion comes from a biblical passage that seems to refer to Lucifer in Isaiah 14:12-
"How you are fallen from heaven, O Lucifer, son of the morning! How you are cut down to the ground, You who weakened the nations!"
The reason this caused so much confusion is that Lucifer actually means "brightest star", a reference to his beauty as an archangel. The passage actually means "O brightest star". The passage is said to be speaking of not Lucifer, but one of two other entities. The first is Samael, The former Angel of Purity, a powerful and pure angel who ruled the order of Seraphim. He stepped down from his post to oversee Hell. This passage is then a lament at the loss of this entity in the brightness of Heaven. Such a movement would certainly shake the nations!
The second possibility is that it references a king of Babylon.
Most occultists and theologians believe that it references Samael.
So Who is Lucifer?
To answer this question, one needs to understand the nature of angelic beings. These entities are spirits, disembodied entities with the power to become solid under certain conditions. As spirits, they embody a very narrow set of experiences. An angel is said to have free will, but not freedom of choice. What this means is that an angel's decisions are absolute. An angel cannot change it's mind once it's made a decision. With this in mind, remember that all angels are tremendously intelligent, able to see the results of their actions far into the future. An angel must choose to "Fall", knowing full well it's fate.
This brings us back to Lucifer, The Fallen Angel. Lucifer was a great and powerful angel, so beautiful that he was like a star. At some point, He got the idea that he could be his own "source", that he could become a god. He was so full of pride that he thought he could move God off His throne, His "place". Lucifer actually thought to make a place for himself ABOVE God. Making this choice, Knowing full well how impudent it was, was the sin of Lucifer, The ultimate sin of pride.
His "revolt" was short lived. He and the angels that followed him were cast out of heaven by mere words from God. Lucifer was the first angel to fall from grace.
What about Satan?
Satan is an interesting figure. The biblical equivalent of Prometheus, Satan gave us the "Gift" of Knowledge of Good and Evil. It has been said that Satan wanted us to experience the joy of good, but to do so we needed to know evil as well. Often portrayed as the ultimate evil, Satan was created to tempt mankind. As the tempter of Man, Satan was supposed to provide an opportunity for man to overcome hardships through faith. This would allow us to grow spiritually and emotionally. Two things led Satan to fall from grace.
The first was Jealousy. Satan became jealous of God's love for Adam and Eve, and so set about a deception that would either make us closer to god or take us further from His presence. This was the forbidden fruit. The result of course was the expulsion of Adam and Eve from the Garden of Eden.
The second, which is tied to the first, is that Satan's methods were closely monitored by God. Satan was only allowed to use methods that God approved of. He was only allowed to go so far and use certain tools. Satan thought that God was too easy on us, that if we were tempted sorely, we would fail and god would turn away from us. Part of his decision to fall was knowledge that god would always be watching him, and without god's tempering hand his methods could be as varied as he pleased. He figured that every time he tempted or corrupted a human, with god watching, his existence would be re-affirmed. He's still doing what he was meant to do, but his leash is off.