Darths tend to have their name mean something about them. Darth Sidious is insidious, Darth Maul is a great fighter, Darth Nihilus (from KoToR) sucks in all life but does not consciously exist as a person any more.
Darth Vader... Vader is Dutch for father and Vader is Luke's father.
All that to wonder: what was Darth Plagus' Sith Theme? Plagues?