Maxperson
Morkus from Orkus
No. It wasn't. He was on that path from the moment Qui-Gon found him as an angry and fearful child. Yoda saw that right away. It wasn't the beheading of Dooku. It was the anger and vengeance behind it that pushed him farther along the path.But presumably killing Dooku was the first big step on the path/in that direction.