You likely knew that the original Emperor Palpatine in 1980's Empire Strikes Back was performed by Clive Revill, but he in fact provided only the audio—as a quick favor for director Irvin Kershner, a friend in need of a cold, unnerving British voice during the movie's edit. What you see is in fact the actress Marjorie Eaton and the superimposed eyes of a chimpanzee.
Such an ingenious and elaborate technical presentation was clearly not viable for the Emperor's longer scenes in Return of the Jedi, hence the casting of Ian McDiarmid, to the character as Anthony Hopkins is to Hannibal Lecter—magnificent, with a larger serving of ham in each new performance.
Revill's brief line, by contrast, suggests a cooly understated Palpatine—would that have worked? McDiarmid was reportedly asked to emulate Revill's voice. He refused and convinced George Lucas and Richard Marquand not to overdub him, writes Chris Agar:
After being cast, McDiarmid immediately made his imprint on the role. Originally, the plan for Return of the Jedi was to overdub the Emperor's voice (like what happened in Empire). Marquand actually told McDiarmid that if the actor could get his voice close to Revill's he may be allowed to keep it. This development surprised McDiarmid, who felt the Emperor should sound different than the previous film. He argued to Marquand that at the time, Revill "didn't really know the character he was playing" and completed his work in quick fashion. Upon seeing what the Emperor looked like, McDiarmid was inspired to craft a voice that sounded like "English upper class and trying to sound like a toad." Evidently, Lucas liked the voice (which became a defining characteristic of the Emperor), and McDiarmid was allowed to keep it.
You know, if someone wants to do a deepfake for the ages, deepfake Marjorie Eaton with chimp eyes into all of Palpatine's classic scenes and have Revill voice it. He's only 92!
