Though I would point out that the title of the leader of the Time Lord state seems to have been "Lord President" -- which I suppose could have been used in conjunction with the title of "Rassilon," but it seems improbable.
Well, I'm just throwing ideas out there. This was a very different Gallifrey than the one we saw before; who knows how many generations had passed, subjectively, or how much they'd been transformed by the unending Time War?
His actions seem to fit what we learn in The Five Doctors, IMO. We learn then that he found a way to cheat death, and that there were rumors and legends about his cruelty.
Except the "cheating death" thing was a trick to lure in the overly ambitious. The "immortality" they were granted turned out to be a trap. Which is why I was wary of the idea that Rassilon had actually returned from the dead in "The End of Time."