who trained palpatine

if there can only be two sith at any one time, a master and an apprentice, who trained Palpatine, i know there are supposed to be dark jedi, but so far there is no evidence to support them and if the sith have been extinct for a millenium how did they manage to come back?

The EU talks of a succession of Masters since the last Sith War; in any case, we can assume that the Sith were never as extinct as others had assumed.

We don't know if Sidious is the latest in a long line or has somehow survived since the the Sith were defeated.

When the Jedi said in the move "The Sith have been exstinct for a millennium" i just felt that they only thought that they were exstinct and the sith were hiding them selves.

That's what I thought as well. We are privieged, as viewers, to know the truth of it.

I think that the JC didn't even bother looking for them, they thought that 'They don't attack us, so they don't life anymore' was at place