2) Emperor Palpatine
Unlike a lot of characters, the Emperor is just as entertaining to watch in both the original and prequel trilogies. If you want a cackling, wizened personification of evil straight from your nightmares, or a more human villain – a scheming politician – then Palpatine is your man either way.
Originally a senator of the Galactic Senate, Palpatine manipulated the political landscape for his own ends – eventually rising to the top of the pile and appointing himself leader of the oppressed, war-torn galaxy. Ian McDiarmid pulls it off in either incarnation of the villain – walking the line between ham and horror in the originals and then as an evil uncle type when he bizarrely plays his younger self even though he’s older in the prequels.
As the uber-villain of both the original trilogy and the prequel (and possibly the revival trilogy as well, if Snoke turns out to be him in disguise), he’s the cause of pretty much all the conflict in the saga. In terms of significance, Palpatine is the greatest Star Wars villain. But, of course, there is one iconic fella who has to come first…