Question Who is "master Sypho Dyas"? as quoted by Obi Wan in episode II?
Answer As you said, Master Sifo-Dyas was mentioned in "Attack of the Clones", wherein he was said to have ordered the creation of the Clone Army at Kamino. Several people probably didn't believe this statement initially, judging by the numerous "Sifo-Dyas" conspiracy theories among Star Wars fans (e.g., Was Count Dooku the actual "Sifo-Dyas" who ordered the creation of the Clone Army? Or was it Qui-Gon, considering that Sifo-Dyas was was killed at about the same time as Qui-Gon?)
Fortunately, the book "Labyrinth of Evil" ended the debate. The book reveals that Sifo-Dyas did indeed order the creation of the Clone Army. In fact, he was a close friend of Count Dooku (when Dooku was still a Jedi). In order for Dooku to pass his Sith trials, Sidious ordered him to kill Sifo-Dyas, as Dooku was told by Sidious that Sifo-Dyas ordered the creation of the aforementioned army. Why would Sidious make such an order? Well, according to the "Revenge of the Sith" picture storybook, Palpatine (the alter ego of Sidious) asked Sifo-Dyas to order the creation of the army. Therefore, it is logical for Sidious/Palpatine to order the murder of Sifo-Dyas, since his plans would deteriorate if Dyas says anything to the Jedi Council or the Senate regarding Palpatine's involvement in ordering the Clone Army.
Thanks for the question. If there are any ambiguities in my response, please feel free to ask again.
