I'm don't know for certain. In the film it seemed like the Jedi knew of a person of that name (though Obi-Wan didn't seem to know him). He died about ten years prior, so around the time of "Phantom Menace". Perhaps he was Palpatine's next apprentice after Maul. Maybe there was a difference of opinion and Palpatine killed him and moved on to Dooku? Who knows.

Wow...you've brought up an unsolved question. Some reports say it was a friend of Dooku who set the order. Sidious, seeing an oppuntunity, told Dooku to kill his friend as a final test. Others say it was Dooku himself, who still had access to the Jedi Temple 10 years before AOTC and placed the order under the fake name of Sifo-Dias. I personally agree with the first. Of course, Kenobi-fan had quite another opinion.

MTFBWY! God bless!

It sounds like Sideous, but the Ultimate Guide says that he was a master who died ten years before, so it can't be a fake name Sideous used.

Your best explanation of Sifo-Dyas is probably found here on Wookieepedia. It even includes an explanation for why "Sifo-Dyas" sounds so much like "Sidious"!

Wow, never saw it that way, that's pretty impressive. Now It seems as though I've seen a much bigger picture lol.

Syfo-Dyas was kept in something like a cryogenic chamber, and was kept in in it untill the creation of General Grievous, Dooku and Sidious transfered his force powers into Grievous. Now wether or not one of hem killed Dyas is another question, and why was he kept in the chamber so long?

His name was actually a ty-po. it was supposed to be Sido-Dyas, It was supposed to be Darth Sidious' real name (like Tyranus is Duku`s), but since he was written into the script They officially made him a character in the comic "The Eyes of Revolution" He was a friend of Duku when he was a jedi still. Sifo-Dyas had a premonition that in time there would be a war and they would need an army, so he secretly commissioned a clone army on Kamino. After Duku moved to the dark side, as a final test of his allegiance, he murdered Sifo-Dyas and took control of the project for himself, but when Obi-Wan Kenobi traveled to Kamino, he was informed that Sifo-Dyas ordered the clone army in order to help the Galactic Republic.