Sifo-Dyas was once a good friend of fellow Master Dooku, and had the gift of precognition. He predicted the coming war, and knew the Galactic Republic would soon face dark times.
Sifo-Dyas secretly commissioned a clone army on Kamino, ostensibly to defend the Republic. Prior to this, Dooku had left the Jedi Order, and had fallen in league with Darth Sidious. He was told by the Sith Master about Sifo-Dyas' actions, and Sidious also revealed that they could use the clone army for their own ends. As a final test of his allegiance to the dark side of the Force, Dooku murdered Sifo-Dyas and took control of the project for himself. It was Sidious' true intention to use Sifo-Dyas only as a dead-end cover for Palpatine's order of a clone army.
Dooku kept his old friend's body frozen for years until the InterGalactic Banking Clan initiated their plan to turn the Kaleesh warlord, General Grievous, into a great cyborg supreme strategist for the Separatist droid armies. Dooku used Sifo-Dyas for a blood transfusion for the General. Once Grievous' transformation into a cyborg had been successfully completed, Dooku gave him the very special gift of Master Sifo-Dyas' own blue-bladed lightsaber.
When Obi-Wan Kenobi traveled to Kamino to investigate the source of the dart that silenced Padmé's attempted killer Zam Wesell, the Kaminoan prime minister Lama Su informed Obi Wan that Sifo-Dyas had ordered the creation of a clone army on Kamino at the request of the Senate, in order to help the Galactic Republic. The Jedi Council was not aware of the order until Kenobi informed them of it after he met with the Kaminoans.
In 22 BBY, Sifo-Dyas' army was eventually revealed and used at the behest of the Galactic Republic. Three years later, it would be used to destroy the Jedi in accordance with Order 66.
[edit] Behind the scenes