Sifo-Dyas was a powerful Jedi Master of the Old Republic. Master Dyas was one of the Jedi Order's most skilled seers. He was also good friends with Jedi Master Count Dooku before Dooku left the Jedi Order. Around the time of the battle of Naboo, Sifo-Dyas' skills in precognition led him to believe that the galaxy was heading into dark times. Master Dyas predicted the galaxy would soon be engulfed by war and the Jedi would be called upon to serve as warriors in the war. He also knew the Republic would need a standing army to meet the threat and took it upon himself to secretly set in motion a plan to build the army the Republic would need.
Surreptitiously, the Jedi Master contacted the Kaminoans of Kamino, some of the best cloners in the galaxy. He commissioned a clone army which the Kaminoans assembled for over a decade following Sifo-Dyas' order. Not long after Sifo-Dyas took this action, the beginnings of those dark times he foresaw began to manifest themselves. Count Dooku left the Jedi Order disillusioned by the stagnancy he felt had corrupted the Jedi Order's effectiveness. Following his desertion, Dooku was seduced to the Dark Side by Darth Sidious, the reigning Sith Lord at the time. While Sifo-Dyas wished his plans to build a clone army to remain secret, such information could not escape the attention of Darth Sidious.
With a new apprentice at his side, Darth Sidious informed Count Dooku, now Darth Tyrannus, of the clone army Sifo-Dyas commissioned. Darth Sidious was close to finalizing his plans to exact revenge on the Jedi and take control of the galaxt, and the clone army could be used to achieve these goals. As a final test that would signify Count Dooku loyalty to the Sith, Darth Sidious ordered his apprentice to murder his old friend, Sifo-Dyas, and take control of the clone army. Dooku complied and murdered Sifo-Dyas making his fall to the Dark Side complete.