A powerful fool that was still out there in my time. I've seen the holos and done my research on the previous Emperor that the New Republic dethroned. He was nothing compared to Vitiate. The destruction of the Hosnian system was done by science, but Vitiate could go through planets with his Force abilities alone. I have yet to meet anyone else who could cause such destruction with their own power.
I'm honestly surprised that he doesn't appear to be the one masterminding the current state of affairs in the galaxy.