A Sith Lord in the Star Wars universe. In the guise of his alter ego, Supreme Chancellor (later Emperor) Sheev Palpatine, Darth Sidious gained leadership of the Galactic Empire through treachery and manipulation. Use this tag with the [star-wars] tag.
Born Sheev Palpatine, he secretly became the apprentice of the Sith Lord Darth Plagueis and took the name Darth Sidious. Publicly, he was the Republic Senator from Naboo until he engineered the Invasion of Naboo as Darth Sidious. The Naboo crisis propelled him to the Supreme Chancellorship of the Republic.
Later, Sidious similarly engineered the start of the Clone Wars between the Republic and the Confederacy of Independent Systems (CIS). Sidious used the crisis of the Clone Wars to gain further power in his position as Supreme Chancellor. Near the end of the Clone Wars, he issued Order 66 to the clones of the Grand Army of the Republic and in doing so nearly exterminated all members of the Jedi Order. Upon the final defeat of the CIS, Sidious transformed the Republic into the Galactic Empire and declared himself Emperor.
Darth Sidious was the master of Darth Maul, Darth Tyranus, and Darth Vader.
Source: Darth Sidious on Wookieepedia