I thought they were like draugr, ancient nords.
What makes them more dragon (...duh) than anthing else?

http://uesp.net/wiki/Main_Page

They were servants of Dragons and worshipped them as Gods.

In days of old, when dragons ruled the earth, there lived mortal men who worsipped the beasts as gods. These dragon priests are long since dead... but something has awoken them from their slumber.

ask google and you shall be answered, or the bethesda forums

They were priests that worshipped dragons. I do not see what is so hard about that to understand.

english is not my native language, so i didn't make the connection priest = worship

oh, sorry about that

Pretty much this. The main difference of them versus the Draugr, are they were the leaders of the Dragon Cult. They were granted masks of great power and were pretty handy with magic. Draugr are more like the soldiers of the Dragon Cult, though some stronger ones (Deathlords) learned shouts.