I always liked Darth Vectivus. The guy was just different. He was one of the first(if not the first) Sith to exist without being a bloodthirsty, single-minded, warmongering hulk, bent on ruling the galaxy or destroying the republic. He was a Darksider and he was evil, but he mostly chilled on his asteroid and as long as the Jedi didn't bother him he wouldn't have to slap a motherkarker. In my opinion having the affinity to not only learn and master Force Phantom but to have the prowess to summon hundreds of them without breaking a sweat? I find that to be quite ridiculous. The One Sith knew of this power but they had no relationship with Vectivus and could never find the means to approach him so they couldn't learn it. However, none of them dared to take it by force either. Nobody karked with Vectivus and he's one of the few Sith Lords to die naturally of old age.
Then after death became a force ghost and later shared his knowledge with Lumiya and blew her mind so hard that she felt that a Sith Lord with the moral stature of Darth Vectivus was necessary to restore galactic stability; and soon afterwards lured Jacen Solo to Vectivus' home and after a short conversation with the Force Ghost, Jacen decided to become Dark Lord of the Sith.