10 MORE Star Trek Villains Who Killed The Most
6. Jetrel
This is a controversial entry, as Jetrel is effectively the Oppenheimer of Star Trek. His work allowed the creation of the Metreon Cascade, which in turn led to a devastating attack against the Talaxians.
The man came aboard Voyager early into the ship's adventure in the Delta Quadrant, which led to a difficult meeting for Neelix. Neelix himself had suffered from Jetrel's work, losing his entire family to the Cascade, though he was off-world, thankfully, when the device was detonated.
Perhaps including Jetrel as a villain is too simplistic. Neelix himself was able to, if not entirely forgive the man, then certainly come to an understanding that there was a difference between a despotic maniac, and a misguided scientist - one who felt extreme remorse for his actions.
It may be best to let history judge men like Jetrel. He certainly was aware of the destructive power of his creation, though he personally didn't push the button. Much as Robert Oppenheimer has a complicated place in the history of humankind, so too does Jetrel in the annals of the Delta Quadrant.