It's hard to imagine anybody other than Ian McDiarmid playing the villainous Sheev Palpatine. However, there was a time when the Sith Lord was portrayed by different actors in the original Star Wars trilogy. So why did George Lucas choose to recast the role of Sheev Palpatine? It may have a lot to do with Lucas' growing vision for the villain.
There is little doubt that Darth Vader towered over the first two Star Wars movies as the main villain. However, it was also suggested in The Empire Strikes Back that the real boss here is Darth Sidious, who only appeared as a hologram. In the film, the Sith Lord was portrayed by Marjorie Eaton, who had to wear superimposed chimpanzee eyes. Additionally, the villain's voice was provided by Clive Revill.
It may have made sense at the time since Palpatine was only appearing as a hologram. However, it is believed that Lucas slowly began realizing that the character is so much more important to the storyline and should be played by an actor who can take the role. After several actor changes, McDiarmid was cast and has been playing the character ever since.
We're not exactly surprised that it took some time for Lucas to realize Palpatine's importance but we're still glad that they found McDiarmid. After all, the Star Wars: The Rise of Skywalker actor made it clear that he could physically take on the role and his voice has been the only true voice of Sidious.
McDiarmid reprised his role as Palpatine in the Star Wars prequels and returned for The Rise of Skywalker last year.