Count Dooku

Dooku trained in the Jedi Order, attained the rank of Master, and taught Qui-Gon Jinn, while he himself belonged to Yoda's line of students. Disillusioned with the Republic and the Order, he left them and returned to his inherited title of Count of Serenno.

He led the Separatist movement, which united systems dissatisfied with the Senate, and turned it into the Confederacy of Independent Systems, which relied on the droid armies of the trade conglomerates. On Geonosis, a duel with him cost Anakin Skywalker his right arm.

In secret he was Darth Sidious's apprentice under the name Darth Tyranus: he recruited commanders such as General Grievous, ordered the clone army on Kamino, and waged the war in his master's interests. He died aboard a ship above Coruscant when Skywalker, at the Chancellor's urging, beheaded him.