The first possibility is that the real villain is Darth Plagueis, destined to become Palpatine's own Sith mentor. Plagueis is a Muun, a humanoid species who can live well over a hundred years.

The Sith who mentored Palpatine, Darth Plagueis the Wise, was of the Muun species. In James Luceno’s Darth Plagueis novel, Plagueis is able to fake his own death after getting stabbed through ...