Sauron is the main antagonist from the series Lord of the Rings.

There's tons of information online if you haven't seen the movies or read the books.  A couple of links for reference are as follows.

http://en.wikipedia.org/wiki/Sauron

http://tolkiengateway.net/wiki/Sauron

http://www.tuckborough.net/sauron.html

http://lotr.wikia.com/wiki/Sauron

Basically he's a Dark Lord who wishes to dominate the wills and minds of all free people.  He's powerful but doesn't show it off for the hell of it.  He tends to work behind the scenes trying to manipulate everyone.

His PB is Eric Bana and he's played by Tyler