"The best of all would be the strongest student, yes? Wisest? Most learned in the ways of the Force? Best of all, Dooku would be! Our greatest student! Our greatest failure."
?Yoda

Count Dooku of Serenno was a legendary Jedi Master in the Jedi Order and was one of the most renowned swordsmen of the Galaxy. He trained notable Jedi such as Qui-Gon Jinn and Komari Vosa during his time as a Jedi. It was said that only Masters Yoda, Mace Windu, and later on, Jedi Knight Anakin Skywalker could have fought on equal terms with him.

Later in life, Dooku fell to the dark side of the Force, disgruntled with the corrupt state of the Galactic Republic, and became Darth Tyranus, the apprentice Dark Lord of Darth Sidious, replacing Darth Maul, and eventually being replaced in turn by Darth Vader.

Taking on his birthright as Count of Serenno and the vast fortune that came with the title, Dooku formed the Separatist movement under Sidious's instruction. As political leader of the Confederacy of Independent Systems he led the organization against the Republic in a conflict that would become known as the Clone Wars.

He was slain in a duel by Anakin Skywalker during the Battle of Coruscant near the end of the crisis that he had helped instigate.