Count Dooku

Once a Jedi Knight, Count Dooku served as Yoda's padawan apprentice, and later on personally trained Qui-Gon Jinn. As a powerful Jedi, he served on the Jedi Council before being seduced by the Dark Side and becoming the new apprentice of Darth Sidious. As a new Sith apprentice, Dooku was called Darth Tyrannus.

Dooku left the Jedi Order and allied with many worlds disastisfied with the Republic, and led a scheme to secede from the Republic. What the Separatists did not know was that Dooku was playing them, as Sidious' apprentice. Before leaving the Jedi, Dooku killed his fellow Jedi Syfo Dius and under Syfo Dius' name, he ordered the creation of a clone army for the Republic.

After formally declaring their movement the Confederacy of Independent Systems, Dooku captured Obi-Wan Kenobi and tried to recruit Obi-Wan to become his apprentice and overthrow Darth Sidious. When Obi-Wan refused, and Anakin Skywalker and Padme Amidala were captured, Dooku ordered them to be executed.

The execution was prevented when the Jedi leading the Clone Army of the Republic attacked. Dooku escaped and was pursued to his ship by Obi Wan and Anakin. In the battle, Dooku severed Anakin's arm, and dueled with Yoda before escaping and delivering plans for the Death Star created by Separatist scientists to Darth Sidious.

Over the next several years, Dooku led the Separatists against the Republic during the Clone Wars. One of his actions was to recruit a general fighting a civil war on his own planet through force. Dooku had his ship blown up, and had him rebuilt as a cyborg called General Grievous, and blaming the attack on the Jedi.

Dooku then led an attack on Coruscant, sending Grievous to capture Chancellor Palpatine (who was secretly Darth Sidious) as part of a scheme to turn Anakin Skywalker to the Dark Side of the Force. On his command ship, Palpatine told Dooku to kill Obi-Wan and fake the fight with Anakin, and Palpatine himself would in the end assist Dooku, and they'd both turn the young Jedi. In the fight, Dooku knocked Obi Wan unconscious, and followed through with the plan, only to realise that Palpatine was using him when he ordered Anakin to kill him.

Dooku was decapitated by Anakin, and his body presumably burned up in Coruscant's atmosphere when the ship was destroyed.