I took the senator for a kindly politician until about halfway through the movie, at which point one of the friends I was seeing it with leaned over and hissed, "That's the Emperor! It's the same actor as in Return of the Jedi, just without the fright make-up!

Huh. I remember the voice -- the voice reminded me of the Emperor, but I figured it was just a coincidence until the senator became a more obvious baddie.