Count Dooku of Serenno, from the House of Dooku is a fictional character from the Star Wars franchise, appearing in Star Wars: Episode II - Attack of the Clones and Star Wars: Episode III - Revenge of the Sith, as a primary antagonist. He was portrayed by Christopher Lee and voiced by Corey Burton in the animated series Star Wars: The Clone Wars and Star Wars: Clone Wars.

In the 2008 animated series Star Wars: The Clone Wars, Dooku is the leader of the Separatists. In addition to sending Grievous and Ventress on missions to antagonize the Republic, he works with the terrorist group Death Watch to give the Republic a reason to send a military presence to Mandalore, which would play in his favor. The plan falls through when Duchess Satine Kryze of Mandalore urges the Galactic Senate to hold off a military force.  In the third season, Dooku is forced to eliminate Ventress to prove his loyalty to Sidious. Ventress survives, however, and works with Mother Talzin to kill Dooku by giving him Savage Opress as a replacement apprentice. During a confrontation between Dooku and Ventress, Savage turns on both. In the fourth season, after defeating Anakin in three separate lightsaber duels, Dooku gets his revenge on Ventress by having Grievous order the systematic genocide of the Nightsisters. Believing both Ventress and Talzin have been killed, Dooku knows the only threat left to him is Savage while sensing his eventual meeting with Darth Maul. In the fifth season, Dooku plays minor roles via hologram in guiding King Rash of Onderon and Grievous taking over Florrum.  In the sixth season, Dooku finds out the clone trooper Tup executed Order 66 prematurely and works behind the scenes to stop the Republic's investigation. He then manipulates the Banking Clan and its representative Rush Clovis into putting all their resources in the hands of the Sith, bringing war to the planet Scipio. The Jedi find a lightsaber belonging to deceased Jedi Master Sifo-Dyas--whom Dooku murdered years earlier--and start an investigation. Sidious forces Dooku to clean up their trail. Dooku confronts Anakin and Obi-Wan on Oba Diah, revealing his alter-ego Darth Tyranus to the Jedi, and they realize that it was he who created the clone army. Some further investigation by Yoda prompts Dooku and his master to perform a Sith ritual in an unsuccessful attempt to break the Jedi Master; Dooku appears to fight Anakin in the illusion, but is executed in a manner very similar to his eventual demise.Answer this question using a quote from the following article:

What does ventress do in retaliation?
Dooku gets his revenge on Ventress by having Grievous order the systematic genocide of the Nightsisters.