Who is Saruman from Unfinished Tales of Numenor and Middle-earth and what is their importance?

Known as the White Wizard, Saruman is the head of the wizarding order. In the third age, he turns to the dark side and plots the downfall of man on Middle Earth. Saruman always has difficulty with Gandalf, and these issues come to a head during the Lord of the Rings Trilogy. He knows that Gandalf is the greater power, and he cannot ever come to grips with that reality.