Dooku was a Force-sensitive human male Serennian who served as a Jedi Master during the waning years of the Galactic Republic and later Count of House Serenno. He became dissatisfied with the Jedi Order and fell to the dark side of the Force, becoming the Dark Lord of the Sith Darth Tyranus. After leaving the Jedi Order, he served as Count of Serenno and Head of State of the Confederacy of Independent Systems during the Clone Wars. He was the second apprentice of Darth Sidious, the Dark Lord of the Sith, whose plan to conquer the galaxy relied on Dooku leading a pan-galactic secessionist movement against the Republic. As such, Dooku immersed himself in the dark side of the Force and worked tirelessly to advance his and his master's Grand Plan while being unaware that he was merely a pawn of his master.
Born in 102 BBY during the High Republic Era, Dooku was taken by the Jedi Order after being abandoned by his family and learned the Jedi arts as the Padawan of Yoda, the legendary Grand Master of the Jedi Order; he went on to take the maverick Qui-Gon Jinn as his own apprentice. A political idealist, the corruption in the Galactic Senate—as well as the traditions of the Jedi—disillusioned him. In 42 BBY Dooku left the Order and returned to his homeworld, where he reclaimed his title of Count and heritage as a nobleman after overthrowing his corrupt brother, Ramil. His former peers believed his decision was misguided but still held him in high esteem. However the Count of Serenno began to secretly conspire with Darth Sidious. After the death of Qui-Gon Jinn at the Battle of Naboo in 32 BBY, and following the duel in the Works which saw the death of Jedi Master Yaddle, Dooku embraced the dark side and adopted the name of Darth Tyranus upon fully becoming the apprentice of Darth Sidious. Throughout the first decade of Sheev Palpatine's chancellery, Dooku used his resources and charisma to recruit entire star systems to the Separatist cause. At the same time, he oversaw the development of two vast armies that would be pitted against each other in the conflict to come: the Separatist Droid Army, which consisted of battle droids manufactured on worlds such as Geonosis; and the Grand Army of the Republic, composed of clone troopers bred on Kamino and modeled on the bounty hunter Jango Fett.
After years of maneuvering the galaxy into a state of war, the Clone Wars began when the newly formed Republic Military invaded Geonosis in 22 BBY. As leader of the Separatists, Dooku delegated military authority to a cadre of subordinates personally trained by himself, including General Grievous and Asajj Ventress. While Grievous was trained only in the art of lightsaber combat, Ventress was strong with the Force, affording her the opportunity to learn the ways of the dark side from Dooku. The Sith, however, remained faithful to Darth Bane's Rule of Two; and as such, Dooku was compelled to betray his disciple after Sidious became suspicious of his own apprentice's intentions. Though he sought to replace Ventress with Savage Opress and later Quinlan Vos, Dooku ultimately remained beholden to his master's will, which would eventually be his undoing.
By the third year of the war, Dooku and Grievous succeeded in abducting Chancellor Palpatine (per Sidious' plan) from the Republic capital of Coruscant in 19 BBY. During the ensuing Battle of Coruscant, he was confronted and defeated by the Jedi Knight Anakin Skywalker, who summarily executed the Count via beheading at the Chancellor's behest. In the days following Dooku's death, Palpatine revealed to the Jedi that he was, in fact, Darth Sidious, who betrayed his apprentice in order to replace him with the younger and more promising Skywalker. With the subsequent fall of the Jedi Order, Sidious consolidated his power upon declaring himself Emperor of the Galactic Empire, which Tyranus had an instrumental role in establishing. As for Skywalker, he succeeded the late Darth Tyranus as Sidious' third and last apprentice, resulting in his transformation into Darth Vader and proving his slain victim's words of sensing fear, hate, and anger.
