[Morthoron]

A tough one, surely (I know, you're not Shirley). Anyway, these are two of the most important characters in the books (for different reasons, obviously, Shirley).

I will have to go with ++Feanor, as almost the entire Silmarillion hinges on his creations and his actions. He is despicable, vengeful, obstinate, but so were many other artistic geniuses in the 'real world'. For instance, Michelangelo was such a cranky so-and-so that he famously snubbed the formidable Pope Julius II, nicknamed 'The Terrible Father'. He literally had to be dragged back to finish the Sistine Chapel (Raphael, who like Da Vinci had a falling out with Michelangelo, said he reminded him of a 'solitary hangman').

So Feanor, the brooding master, called down the heavens to witness his folly, for he loved too much the work of his hands; and the course of Middle-earth was forever changed.