How does Palpatine change from looking like he does in the PT to the OT?

There are 3 posibilities I can think of.

1. He always looked like the Emperor from ROTJ, but somehow uses the dark side to disguise himself so he looks like a noble senator?

2. He gets disfigured in the duel with Yoda?

3. He gets disfigured in Anakin's "dark rage" fit when Anakin learns he has killed padme?