Asper Argo Commdor
The Commdor is the leader of Korell. Sure, he'll accept the Foundation's help to increase the strength of his country. But just so you know, he's planning on stabbing you in the back—gaining support from the old Galactic Empire to attack Terminus as soon as his armada reaches great enough power. Bit of a turncoat, this one.
This starting to sound familiar? If it does, that's because the Commdor is the Wienis of "The Merchant Princes." To say their roles are very, very, very similar would be an understatement. You'd need to write in very at least two more times.
Both men claim to be attacking the Foundation for the benefit of another while they're secretly planning to take all that lovely ruling power for themselves. Both men also try to outsmart their respective Foundation leaders only to lose due to pressures of the people they are supposed to rule.
Oh, and both men are just kind of all-around unlikeable.
To be fair, the Commdor is slightly different. First, he learned his lesson after seeing what happened to the Four Kingdoms. Unlike Wienis, the Commdor understands the purpose of the Foundation's spiritual power and wants nothing to do with it.
So, unlike other antagonists, he's willing to change his plans according to that information, making him the most rational-thinking of the antagonists. He just isn't willing to find a way to change his country itself, believing he can gain strength by assuming the technology of others rather than promoting the technological growth of his own people. This gives Mallow room to outmaneuver him with the Foundation's super innovative economy.
Second, the Commdor's violence is kind of passive. Wienis is more than willing to shot his opponent right in the face while the Commdor prefers someone's back. (It keeps the victim from being so squirmy.) But he'd really much rather just send someone else to do the dirty work.