Count Dooku

He was seen battling Yoda who called him his "old padawan." Then Dooku toppled a piece of the building and escaped his ship. Then Yoda used the piece to crush the ship. He was later seen in a hologram in chains. The republic had found the plans he was carrying for the Death Star. 3 years later, anakin put 2 lightsabers around his neck and Palpatine told him to kill Dooku. Ki Adi Mundi refused to let anakin join the council because Dooku told Obi Wan that Dooku said the senate was under control by the sith.

Appearances

How attack of the clones should have ended

how revenge of the sith should have ended {flashback}