Who was Lucifer and what did he do?
Lucifer was not a fallen angel of vague legend but a brilliant administrator, a created Son who ruled a system of inhabited worlds. The Urantia Book records that unrighteousness was found in him, and his rebellion against God’s government swept up our planet, whose isolation shapes human history still.
In the book's own words
Lucifer was not an ascendant being; he was a created Son of the local universe, and of him it was said: “You were perfect in all your ways from the day you were created till unrighteousness was found in you.” Many times had he been in counsel with the Most Highs of Edentia. And Lucifer reigned “upon the holy mountain of God,” the administrative mount of Jerusem, for he was the chief executive of a great system of 607 inhabited worlds.
The better next question
Was the Garden of Eden a real place?