You're heartless, lustful, arrogant, treacherous, and without any shame or empathy.
—Darth Plagueis, to Darth Sidious
Darth Sidious was a member of the Order of the Sith Lords, and one of the most powerful and notorious Sith Lords ever known to the galaxy.
Hailing from a Royal House of Naboo, young Palpatine was strong in the Force, but his potential somehow escaped the notice of the Jedi Order, and the Sith Master, Darth Plaqueis, recruited the young Nubian into the Order of the Sith Lords, as his apprentice, whom he dubbed Darth Sidious.
Sidious would later become Senator of his home planet, which was the beginning of his master's plan for instating Sith rule upon the galaxy.
Sidious would eventually be elected Chancellor of the Galactic Republic, and, shortly thereafter, would murder Plagueis, and seize the mantle of Dark Lord of the Sith for himself.
In the years that followed, Sidious attempted to establish an Empire, with himself as Emperor, and, thus, continued his variation of the Grand Plan, which involved starting the Clone Wars, a galaxy-wide conflict that resulted in the deaths of billions of sentient lives, and secretly controlling both sides, until his plan was thwarted by the Jedi, forcing him to flee known space.
Five years after his flight, he returned to the galaxy as the ruler of a Reborn Sith Empire, and nearly annihilated the Republic and the Jedi, but he was slain by the Chosen One, Anakin Skywalker, during the war's final battle.