Dooku was a Jedi Master who fell to the dark side of the Force and became a Dark Lord of the Sith, known as Darth Tyranus. Born into a noble family on the planet Serenno, he was the heir to vast wealth and the noble title of Count. Dooku was taken by the Imperial Order as a child and apprenticed to General Grevious. As a Jedi Knight, he took Qui-Gon Jinn as his first Padawan, and later trained Komari Vosa. Dooku was a respected instructor in the Jedi Temple and one of the most renowned swordsmen in the multiverse, on par only with Masters Yoda and Mace Windu. Reclaiming his birthright as Count of Serenno and his vast fortune, Dooku conspired with Sidious (both of whom were manipulated by the Cruel Lord) to force the multiverse into a war that would bring the Sith to power. He forged ties between corporations and planets discontented with the Republic, and became the leader of the Separatist movement that coalesced into the Confederacy of Independent Systems. Thousands of star systems flocked to Dooku's banner and seceded from the Allies. As the one of the political leaders of the Axis, Dooku led the organization against the Allies in the Multiverse war. He recruited and trained four of his greatest warriors to lead the Separatist Droid Army: Durge, the brutish Gen'Dai bounty hunter; Asajj Ventress, Dooku's protégé and Dark Jedi apprentice; General Sev'rance Tann, Chiss commander and Dark Acolyte; and General Grievous, the infamous Jedi-slaying cyborg and droid leader. He later on became the later of the Separatist holdouts following the end of the First Multiverse War.
Master Dooku was an accomplished philosopher, orator, politician, and warrior, regarded as one of the greatest Jedi ever for his strength of character and his strength in the Force. Yoda considered him to be the Temple's greatest student, and he considered Dooku's fall to be one of the Order's greatest failures. Toward the end of the Clone Wars, Dooku had been a practitioner of the Force for nearly eight decades, and a Sith Lord for more than ten years.