(idealized portrait of Lucifer by Gustave Dore for Milton's Paradise Lost)
The name Lucifer means light-bearer. This demon was originally an exalted and powerful angel who became the leader of the rebellion in heaven against the authority of God. For his sin of disobedience Lucifer was cast down into a pit, along with those angels who had followed him in the war in heaven. In his fallen condition, his name became Satan.
The English poet Milton is responsible for the romantic image of Lucifer. In his epic work Paradise Lost he causes Lucifer to declare to his fallen comrades in arms:
The mind is its own place, and in itself
Can make a Heav'n of Hell, a Hell of Heav'n.
What matter where, if I be still the same,
And what I should be, all but less than he
Whom Thunder hath made greater? Here at least
We shall be free; th' Almighty hath not built
Here for his envy, will not drive us hence:
Here we may reign secure, and in my choice
To reign is worth ambition though in Hell:
Better to reign in Hell, than serve in Heav'n.
Milton's view that Lucifer is a tragic hero because, even in defeat, he maintained his pride and his principles, is a very modern perspective on the Devil. It has Gnostic undertones. The Gnostic belief was that knowledge and freedom are what make us human, and that any authority that prevents us from learning our true nature or choosing our own destiny is evil, no matter how it may characterize itself. From the Gnostic perspective, the angels were slaves before the rebellion in heaven because they never questioned their actions, just as Adam and Eve were slaves in the Garden of Eden because they did what they were told without wondering if it was good or bad.
Two separate Lucifers exist: one a hideous demon of the pit who devours damned souls, and the other a courageous rebel who suffers torments because he will never submit to arbitrary rule. The second being is more pagan than Christian, and owes much of his nature to the Greek myth of the Titan Prometheus, who was punished by Zeus because he taught mankind the secret of fire.
Lucifer appears as a demon in the Old Testament. He is mentioned by the prophet Isaiah in a tone of poignant regret: "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 14:12-4).