George S. alerts us to a guide to the villains of AOTC from Newsweek:

Count Dooku and Darth Sidious are the two main bad guys?
Right.

And Sidious is ... who?
The wrinkly guy in the cloak at the very end. Remember the Emperor from the original trilogy? That?s him.

And Chancellor Palpatine, is he evil?
Probably. We don?t know for sure yet, but it?s pretty clear that Palpatine and Sidious (and, hence, the Emperor) are the same guy. The clue is that they all have the same voice.

Why does Dooku build a Clone army and a droid army for Sidious?
Sidious needs a reason for the Republic to raise an army, so he creates a false threat: droids. Their sole purpose is to get steamrolled by the Clones.