Darth Sidious (born as Sheev Palpatine and also known as the Emperor) is a fictional character from the Star Wars universe. He is the main villain of the Star Wars movies. His most famous power, seen only once, is force lightning seen in the last episode Return of the Jedi which is forked to spread the damage even further and is blueish purple.
He is played by Ian McDiarmid. He is seen in Episode V for the first time. Darth Sidious is regarded as the true villain of the Star Wars films because he was the one who caused Anakin Skywalker to join the Dark Side of the Force.
In Episode I, The Phantom Menace, he is a Senator from the planet of Naboo. He is also secretly a Sith Lord, Darth Sidious. Sidious pulls the strings behind the scenes to cause unrest and dispute in the corrupt Galactic Senate, hence the films' title. His apprentice during this time is Darth Maul, who is slain in battle by Obi-Wan Kenobi. At the end of Episode I, he has risen to the office of Supreme Chancellor and begins his rise to power.
In Episode II, Attack of the Clones, Sidious secretly continues to bring the galaxy to civil war. He has a new apprentice, Count Dooku, who leads the Separatist Droid Army and goes by the name 'Darth Tyranus'. Dooku is slain by Anakin Skywalker on a rescue mission to free the Chancellor in Episode III, Revenge of the Sith.
Sidious rose to complete power in Episode III, when he sent Anakin to lead an attack on the Jedi Temple and ordered the Clone Troopers to execute Order 66, killing many Jedi in the process. Sidious battled Yoda in a duel which would decide the fate of the Galaxy. He narrowly defeated Yoda, and was able to form a new order upon the fallen Republic. He created the first Galactic Empire. In the time frame from his creation of the Empire and his death, Sidious was a cold, merciless Emperor. He ruled through fear. His evil was staggering as he dominated the galaxy with his ruthless enforcer, Darth Vader.
Since the initial theatrical run of Return of the Jedi, Sidious has become a widely recognized symbol of evil in popular culture, and since the prequel films, also one of sinister deception and the subversion of democracy.