I'll say Adrik Thorsen from Federation, for sheer nastiness and persistence.
I remember that now! I used to listen to Mark Lenard's audiobook of that.
They tied that into the WWIII setting didn't they? Those red eagle flags seen during the courtroom scene from
Encounter at Farpoint, would've belonged to the Optimum and Adrik Thorsen was their leader? John Burke featured in that too but no Colonel Green. Adding that to detail from
First Contact, would seem to imply certain sections of the Western world became facist and the opposing side was the ECON? Is that right? Eastern Coalition? Okay that's a cheat since Federation was Judith & Garfield Reeves-Stevens original explaination, before the film became the established version of the mid-late 21st Century.