He is the pinnacle of all evil it seems. But he is really the victim.
Once Anakin Skywalker, the boy with exceptional skills who was selfless and innocent as a child. His skills made him arrogant as he got older. He was reckless and didn't abide by Jedi rules This led to him
falling in love with Padme Amidala.
He feared losing her, and as Yoda said,
'Fear is the path to
the dark side. Fear leads to anger. Anger leads to hate. Hate leads to suffering.'
He went to
the Dark Side in order to save his wife, everything he ever does he believes he's doing for good.
He is the Chosen One, the one who brings the force back into balance.
Also father of Luke and Leia.
The whole of the Star Wars saga is about the tradgedy of Darth Vader.
(Plus he kicks ass!)