Paradise Lost was originally a collection of twelve books based on the biblical stories about the revolt of Satan against God, and Satan's corruption of Adam and Eve in the garden of Eden.
Nicholas Meyer decided that while Khan had been waiting for a chance to avenge himself upon Kirk, he would have been reading. "I started thinking, 'What books does a superman take with him into exile?' At one point, Khan says, 'On Earth I was a prince', and certainly he's a fallen angel, so I picked all the books that were Lucifer-related – fallen angel – whether it was 'Moby Dick' or 'Paradise Lost' or 'King Lear', and began to build from there. I thought, 'He's probably been obsessively reading these books again and again until every word out of his mouth has been written by Shakespeare or Milton'. Actually, Melville was the one who finally took over; he just becomes completely Ahab."