Like all Sith, Sidious and Dooku constantly tested each other as master and apprentice. Disturbed by his apprentice’s relationship with Asajj Ventress, Sidious contacted Dooku on Serenno and ordered him to betray and abandon his assassin. Dooku reluctantly agreed.

Ventress survived her master’s betrayal and plotted with Dathomir’s Mother Talzin to get even with him. She led a team of Nightsister assassins to Serenno. Cloaked by spells, they attacked Dooku but failed to kill him.

Talzin then contacted Dooku on Serenno and offered him a Nightbrother from the far side of Dathomir to replace Ventress as his servant. Wary after his close call, Dooku agreed to the Nightsister matriarch’s offer.

Talzin arrived on Serenno with Savage Opress, a massive warrior. Little did Dooku know that Savage had been handpicked by the Nightsisters and shaped into a killing machine meant to betray the count.

Dooku took Savage as his new apprentice, brutally training him in lightsaber combat and the ways of the dark side.

Dooku’s regimen was harsh and pitiless for a reason – Savage would only unlock the power of the dark side of the Force by allowing himself to be consumed by fear, rage, and pain.

Having taught Savage to draw upon the dark side for power, Dooku sent him from Serenno to destroy the count’s enemies. Savage killed King Katuunko on Toydaria and massacred the Temple of Eedit’s defenders on Devaron before fleeing a three-way battle with Dooku and Ventress and seeking refuge in the Outer Rim.

As part of an elaborate plot of Darth Sidious’s, Dooku summoned some of the galaxy’s best bounty hunters to compete in a test of skill. The contest was held on Serenno, in a treacherous facility created by Moralo Eval and known as the Box.

The hunters who passed Dooku’s test were Derrown, Embo, Twazzi, Cad Bane and Rako Hardeen (secretly a disguised Obi-Wan Kenobi). The hunters and Eval then traveled from Serenno to Naboo, where they planned to kidnap Supreme Chancellor Palpatine.

Dooku had not forgotten his betrayal by the Nightsisters. He summoned General Grievous to Serenno and ordered him to lead a massive assault on Dathomir, destroying Talzin’s clan.

Grievous did as instructed, but the Nightsisters used their magic to inflict terrible pain on Dooku, reaching across the light-years between Dathomir and Serenno. The count was saved when Grievous killed the Nightsister matriarch Old Daka, breaking the spell.

When a clone trooper’s implant malfunctioned, causing him to murder his Jedi General, Dooku worked frantically on Serenno to prevent the Jedi from discovering the true purpose of the clone armies they led. Dooku contacted the Kaminoans, directing them to hide evidence from the Jedi.

The Sith managed to keep the Jedi in the dark about the clones’ purpose, but Sidious flew into a rage when the Jedi discovered clues to the fate of Sifo-Dyas, the long-dead Jedi in whose name the clone army had been created. Sidious used the Force to choke Dooku in his sanctum on Serenno so he understood the price of failure.

After Quinlan Vos and Ventress failed to assassinate Dooku on Raxus, the count captured Vos and took him back to Serenno, where he tormented him in hopes of turning him to the dark side.

Ventress hired Boba Fett’s crew of bounty hunters to help rescue Vos from Serenno. The rescue mission succeeded, but Vos had seemingly been seduced by Dooku. A heartbroken Ventress fled Serenno with the hunters she’d hired.