Star Wars: Every Jedi Who Turned To The Dark Side

Count Dooku was abandoned, as a child, by his family. He was scooped up by the Jedi and trained as a Padawan by the Grand Master Yoda. Later in life, Dooku would become disillusioned with both the Jedi and the Galactic Republic, seeing both organizations as unresponsive to the needs of the people they each claim to serve.

One instance that highlights Dooku's disillusionment would be the Force vision of Dooku's close friend, and fellow Jedi, Sifo-Dyas. At some point, Sifo-Dyas informed Dooku that he'd had a Force vision of a deadly solar storm that threatened a planet called Protobranch.

Of course, Dooku and Sifo-Dyas went to the Jedi Council to warn them of the oncoming disaster. The Council, led by Yoda, informed them that they would not be allowed to warn the leaders of Protobranch. The Council's reasoning for not warning Protobranch- they were like, "eh, sometimes visions are wrong."

Needless to say, Dooku did not accept this reasoning and warned the senator of Protobranch, a man named Tavetti. To Dooku's horror, Tavetti was more concerned about the potential property damage than human life loss. Ultimately, the predicted solar storm occurred, killing much of Protobranch's population. This was just one of many instances that made Dooku reconsider his devotion to the Jedi and the Republic.