(I'm guessing by "evil" he would mean selfish and malicious. Someone can have the best of intentions, can honestly think they're doing the right thing, and still be evil. I was researching an alternate-history project in high school and college and, while reading about the Russian Civil War, learned about Cheka founder Felix Dzerzhinsky. According to future Polish leader Józef Piłsudski, who went to school with him, Dzerzhinsky "did not know how to lie," another source described him as being strict toward himself as well as others, and the quotes I found indicated he was wracked by guilt about the horrors he oversaw as the Bolsheviks' hatchet-man.)
A long time ago I discovered the quote that "everybody is the hero of their own story." I have taken pains to apply the principle when I write villains, and I cited it before in my blog post about Roose Bolton from the fantasy novel series A Song of Ice and Fire and its HBO adaptation A Game of Thrones. Dzerzhinsky thought he was building a utopia and that would justify breaking a few (or many) eggs along the way, while Roose Bolton could justify his treachery against Robb Stark by claiming it in the best interest of the North and the realm as a whole that the Lannisters win as quickly and bloodlessly as possible. The warlord Grendel of my Wastelands series wants safety, security, and power (to better ensure the first two) for his family and friends--which he seeks through imperialism and aggressive warfare. Meanwhile, the cult leader Phil from my Lovecraftian novel The Thing in the Woods wants to protect the town of Edington from corrupting outside influences--which he does by kidnapping people he doesn't like and feeding them to an alien monster.
And now we get back to Star Wars. One of the most interesting blog posts I've ever found was called "The Tao of Sith" and was posted on a blog that's essentially the events of The Empire Strikes Back and Return of the Jedi from the point of view of Darth Vader, Dark Lord of the Sith and apprentice to the Emperor Palpatine.
(The post initially went to some "Star Wars Webring" site, but I clicked on it again and it went to the right place, so have faith.)
The gist of it is that Vader believes the Sith were justified in their various misdeeds and creating the Empire because galactic civilization was in danger of collapse. Furthermore, the Jedi were neglecting their responsibilities and denying their emotions in favor of idle contemplation except in a few circumstances ("trivia that offends their effete sensibilities"), despite allegedly knowing that "an age of barbarism" was nigh. The Sith, in contrast, embrace life, embrace emotions, and embrace the actions necessary to save civilization.
(Given how the prequel-era Jedi demanded their adherents forsake emotional attachments, relationships, etc. a lot of Vader's comments ring true.)
Vader as depicted in the blog post is NOT a simple monster using politics as a cover to indulge his appetite for sadism, power and control, etc. My article on how fictional villains should not be sociopaths acknowledges such people exist, but they don't make for interesting bad guys (or girls). So if you're writing a villain, try to see things from their point of view. What is their story, and why are they the hero in it? Not only will you have a much better-developed villain, but you might also have a much varied and "grayer" world if it turns out the villain has some good points.