Well, by the TOS definition, breaking the law is the same thing as being mentally ill, so that doesn't tell us much. (But Garth bellowing "
Lord Garth!!" is telling enough.)
What's this thing about Tracey starting a war? He started nothing - the Yangs were slaughtering the Kohms when he arrived. And killing, oh, a thousand Yangs shouldn't even register on the scale of evil, considering how many the Yangs had killed so far (that is, every single Kohm on the planet, save for those Tracey protected). It's just too bad Kirk didn't agree to wiping out the evil Yang once and for all.
Yes, Khan's villainy was of the bloodless sort. He had a soft touch and a smooth turn of phrase in general, and he was the one who made the choice not to kill Kirk and the rest of the bridge crew. But he did appear to think he had succeeded in killing Kirk in the pressure chamber - and we have no idea what his designs for the crew were, once his capture of the
Enterprise would be complete.
Since Kirk was an admirer of Khan, the villain couldn't be too villainy, lest Kirk's credibility be ruined. Perhaps Kirk got the idea of marooning Khan from the master himself, that is, Khan's plan had been to strand Kirk's 430 crew on a habitable planet?
(He did maroon the crew of the
Reliant if we can believe Chekov, rather than killing them - and that was the crazy version of the man. Khan, I mean, although admittedly Chekov wasn't in complete control of his faculties, either.)
Hmm. My vote for the biggest villain goes collectively for everybody who survived "Metamorphosis", that is, contributed to feeding Nancy Hedford to the Companion...
Timo Saloniemi