The scariest characters in the LOTR?

I agree with what was said about certain settings becoming the scariest moments of all in the Lord of the Rings.

I disagree with the whole Sauron isn't scary because he does nothing and you never see him thing.

I take Sauron and the ring together as one huge, invisible evil, an evil that can as someone here said, turn your friends like Boromir against you. What could be scarier then that invisible evil, and knowing that the only way to stop it is to destroy the ring itself, which holds the greater part of Sauron's power.