2. Darth Malgus

 Darth Malgus served the ancient ideals of the Sith better than any other, especially at a time when the Empire was seeking to make a deal with the Republic. As such, while he desired power, he also wanted to see all of his order’s traditional enemies obliterated.

This desire led him to establish his own Empire, although that effort wasn't completely successful. In his quest for perfection, he identified and quickly eliminated his weakness, which turned out to be his own lover (an interesting twist that we haven't seen in the movies).

As an actual tank, Darth Malgus withstood punishment like no other, although he did come away from his fierce battles against the powerful Jedi with some scars. Nonetheless, he did survive the conflict.

Darth Malgus was a skilled lightsaber fighter, and many agree that he was virtually invincible in a one-on-one confrontation. His use of the Force further enhanced his talents. Unlike other Sith Lords on this list, it took a Jedi strike force made up of the most powerful Jedi masters to kill him.