So when he heard what happened, he was immediately filled with sadness and anger, leading him to leave the Jedi Order. as he knew Qui gon's death could have been avoided.
When Qui-Gon was killed by Darth Maul, Dooku was so saddened that Qui-Gon's death lead to Dooku's transformation into the Sith Lord Darth Tyranus. He would later provoke the memory against Obi-Wan Kenobi, Jinn's apprentice.
You can also see how much Qui Gon Jinn's death affected Dooku when he was talking to Obi Wan in AOTC. Look at the raw, pure emotion Dooku feels over a decade after Qui-Gon died. It affected him significantly.
Jinn's former master, Count Dooku, had been considered to attend the funeral but had declined the invitation, claiming he would not be "pleasant company".
Count Dooku Mourns Qui-Gon Ginn | Star Wars: Tales of the Jedi
Would Dooku have turned if Qui-Gon was alive?
Dooku, AND Anakin, would be less likely to fall to the dark side if Qui-Gon was left alive and Maul's sympathetic past would never be revealed. For the former, Order 66 wouldn't be executed since Dooku wouldn't be the one planning to do that on the clones.
Implying to Jedi Master Yaddle that he held the Jedi Council partly accountable for Qui-Gon's death, Dooku refused to attend Qui-Gon's funeral on Naboo.
Dooku is 69. 32 BBY: The events of The Phantom Menace (Qui-Gon's death by Maul), and Sifo-Dyas's death from the Pykes as ordered by Dooku (per Star Wars: The Clone Wars: Character Encyclopedia) in the same year. Dooku is 70.
Although Qui-Gon never felt close with him, Dooku was quite fond of his former pupil, and Jinn's death on Naboo devastated him. The 2012 Legends novel Darth Plagueis showed Dooku's gradual fall to the dark side in detail, and his feelings on the death of Qui-Gon contributed to this fall from grace.
With a potential Jedi Code-defying love affair with another Jedi, Dooku is more of a foil to his Clone Wars-era enemies, Anakin Skywalker and Obi-Wan Kenobi, with Dooku's lover, Jedi Master Jocasta Nu, possibly retaining feelings for Dooku well after he joined the ranks of the Lost Twenty.
An enraged Dooku began Force-choking Dagonet with the intent to kill him, but Qui-Gon released Dagonet's son and managed to defuse the situation without any further violence. In the aftermath, Dooku commended Qui-Gon's actions and praised him as a wiser man than him.
Because Maul punched him with the hilt of his saber and then stabs him faster than Qui-Gon can pull back his blade. So Qui-Gon lost because Maul was physically stronger and quicker than him. Qui-Gon is skilled but not a prodigy. And he's quickly worn down by Maul in both their encounters.
Why did Dooku join the Sith when they killed Qui-Gon?
Once a Jedi -- trained by Yoda -- he became disillusioned with the Jedi Order and thirsted for greater power. Dooku voluntarily left the light side behind and became Darth Sidious' dark side disciple, taking the secret name Darth Tyranus and leading the Separatist army.
Did Dooku turn to the dark side because of Qui-Gon?
Dooku's reaction to Qui Gon's death in Tales of the Jedi was so potent, because it pushed him even further towards the dark side, although he was already sort of working in tandem with Palpatine.
In the Star Wars prequel trilogy, the Jedi Order learned that Count Dooku was a Sith Lord in the film "Star Wars: Episode II - Attack of the Clones." The revelation occurred during the course of the movie's events, which were set approximately ten years after the events of "Star Wars: Episode I - The Phantom Menace."
Affiliation(s) Katri was a Mirialan Jedi Master and member of the Jedi Order's Jedi High Council. Between 68 BBY and 42 BBY, she was killed by a group of security guards on Raxus Secundus, and her death was investigated by Jedi Masters Mace Windu and Dooku. Her seat on the Jedi Council was awarded to Windu.
In fact, he even planned on replacing Palpatine before Order 66. Out of all the Sith seen throughout Star Wars, Count Dooku still stands apart from them all. While he was undoubtedly evil, he often had a calm politeness rather than maniacal behavior.
Count Dooku's real name, Dooku, was more fitting than his Sith title, Darth Tyranus, as it speaks to his manipulative nature. Dooku played a crucial role in weakening the Jedi and the Republic from within, planting doubt and eroding trust.
The two were able to free Maul after he had been interrogated by the Sith Lord Count Dooku, and together the three rendezvoused with more Death Watch forces on the moon of Zanbar. Maul took command of his forces once again, and assured them that the war they had longed for was at hand.
Obi-Wan is good at letting his emotions go. He feels them in the moment, the anger and sadness over deaths of ones he loved like Qui-Gon and Satine. The guilt and pain over Anakin's turn. He feels them deeply, and then lets them go.
Qui-Gon: I cannot. My training was incomplete. As such, he can only ever materialize as a disembodied voice in the physical world. The other Jedi who have achieved oneness with the Force have disappeared upon death, such as Yoda, Obi-Wan, and Luke.
