Dooku

Dooku (also known as Darth Tyranus) was Darth Sidious' second apprentice. He served as the founder of the Confederacy of Independent Systems.

Background
Dooku formerly served as a member of the Jedi Order who was the Master of Qui-Gon Jinn. However, Dooku left the Order after the death of Jinn.

At some point prior to 22 BBY, Dooku became the second Sith apprentice of Darth Sidious (publicly known as Supreme Chancellor Palpatine). As part of Sidious' plan to dominate the Galaxy, Dooku established the Confederacy of Independent Systems.

Separatist Crisis
During the Separatist Crisis, Dooku chaired a meeting on Geonosis between several politicians and businessmen who allowed their organisations and planets to join the Confederacy.

Clone Wars
Dooku attended the execution of Anakin Skywalker, Obi-Wan Kenobi and Padmé Amidala. However, the Grand Army of the Republic arrived and rescued the three. This led to the Battle of Geonosis, the beginning of the Clone Wars.

Three years later, Sidious faked his capture at the hands of Dooku and Grievous and was held onboard the Invisible Hand.

Death
During the Battle over Coruscant, Sidious was rescued by Skywalker and Kenobi, who duelled Dooku with their lightsabers. Dooku lost the duel between the two Jedi. Sidious ordered Skywalker to kill Dooku. Skywalker hesitated by ultimately obeyed the Chancellor's orders and decapitated Dooku.

Skywalker succeeded Dooku as Sidious' apprentice shortly after.

Appearances

 * Star Wars: Attack of the Clones (First appearance)
 * Star Wars: Revenge of the Sith