Darth Sidious is the name assumed by Palpatine when he became a Sith Lord. In time, the Sith identity became more real than Palpatine's public face. After the Clone Wars and his ascension to Emperor, Palpatine essentially lived as Sidious for the remainder of his life.
It was Sidious who executed the long-percolating plan of supplanting the Republic with a new Sith Empire. Sidious subverted democracy in the galaxy, and made the Jedi enemies of the state.
Using his Sith skills of manipulation, Sidious masterminded the Clone Wars and most of the events that led to his public persona, Palpatine, becoming Supreme Chancellor and eventually Emperor.
Darth Vader pledged his loyalty to Darth Sidious as the Clone Wars came to an end. Kneeling before his dark master, Vader assumed the mantle of Dark Lord of the Sith. His first assignment was to wipe out the Jedi Temple. After Vader was defeated by Obi-Wan Kenobi and suffered severe injuries, his power was diminished. Darth Sidious rebuilt his apprentice, but kept his sickly yellow eye open for another who could take his place.
As the reigning Dark Lord of the Sith, Darth Sidious is a sworn enemy of Yoda. As Sidious plotted to take over the galaxy, he knew that he would one day have to eliminate Yoda. Shortly after Sidious declared himself Galactic Emperor, he battled Yoda in a destructive duel in the heart of the Galactic Senate chambers.
Darth Sidious arranged for the Trade Federation, under Nute Gunray's rule, to blockade and invade the peaceful planet of Naboo in protest over increased taxation from the Senate. Sidious never contacted the Neimoidians directly. Instead, he relied on holographic communication.