Wikipedia
Sheev Palpatine (also known as Darth Sidious or simply The Emperor) is a fictional character of the Star Wars universe, mainly portrayed by Ian McDiarmid. In the original trilogy, he is depicted as the aged, pale-faced and cloaked Emperor of the Galactic Empire. In the prequel trilogy, he is portrayed as a charismatic Senator from Naboo who uses deception and political manipulation to rise to the position of Supreme Chancellor of the Galactic Republic.
Though outwardly appearing to be a well-intentioned public servant and supporter of democracy prior to becoming Emperor, he is in fact Darth Sidious, the Dark Lord of the Sith – a cult of practitioners of the dark side of the Force previously thought to have been extinct in the Star Wars galaxy for a millennium. As Sidious, he instigates the Clone Wars, nearly destroys the Jedi, and transforms the Republic into the Empire. He also corrupts Anakin Skywalker to serve at his side as Darth Vader. Palpatine's reign is brought to an end by Luke Skywalker and the redeemed Anakin Skywalker.
Since the initial theatrical run of Return of the Jedi, Palpatine has become a widely recognized popular culture symbol of evil, sinister deception, tyranny, and the subversion of democracy.