The Evil Eye is a Eye-Ball like creature that resided on the top of Barad-dûr and was controlled by Sauron, the ruler of Mordor. The Evil Eye is also the most popular representation of Sauron, but Sauron just controls it. It is known as The Eye of Sauron in the Silmarillion and the Peter Jackson movie trilogy, but known as the Evil eye in the Lord of the Rings books.
After Sauron arose in Mirkwood without a true physical form, he took a actual Maiar human like form, but he could be never be actually seen through mortal eyes, so he created the Eye on Barad-dûr to give out the speaking and representation.
Powers and Abilities
The eye had a very powerful ability indeed; if he looked directly into a normal mortal they would have murderous pain, or sometimes death. While this can happen, it also freezes the enemy right there so they won't move.
"You cannot hide.......I see you......There is no life in the void...only...death..."
Sala Baker voiced the eye in the Peter Jackson film trilogy. The Eye's voice's very low and darkish, along with a few hisses with every word.