system
Given the following post, respond as if you're commenting on Reddit:
human
[StarWars] I remember reading somewhere that Count Dooku turned to the dark side because of the death of Qui-gon Jin. Is this true? If yes, why did he ally himself with the master of the guy who killed him?
gpt
It's... not entirely true.

In Legends, the continuity that was ended in 2014, Dooku had already been dissatisfied with the state of the Republic and the Jedi. With Qui-Gon's death, he finally had enough and left the Jedi, seeking out the Sith... but remember, Palpatine is very intelligent and charismatic, and he recognized that Dooku would be useful to his goals and sweet talked him into joining.

In canon, for the timeline of events as shown in The Clone Wars to work out, he actually joined with Palpatine before the events of The Phantom Menace, and just used Qui-Gon's death as a cover to leave the Jedi and join the Sith.