Here is what I would consider my top ten:
10. Uchida, the Gangster - The H-Man (Makoto Sato)
9. Lance Corporal Sudo - The Secret of the Telegian (Tadao Nakamaru)
8. Makoto Obata – Yog, Monster from Space (brilliantly played by Kenji Sahara)
7. Malic – Latitude Zero (juicy role for Cesar Romero)
6. Malmess, the Assassin – Ghidrah, The Three-Headed Monster (Hisaya Ito)
5. Kumayama, the great entrepreneur – Godzilla vs. The Thing (wonderfully played by Yoshifumi Tajima)
4. Mami Sekiguchi the Singer – Matango (seductive Kumi Mizuno!)
3. Dr. Who, Megalomaniac – King Kong Escapes (Eisei Amamoto, in probably his most famous role).
2. Shiro Torahata – Godzilla vs. The Thing (Kenji Sahara at his most baddie!)
And
1. Clark Nelson, evil entrepreneur, tomb raider, etc – Mothra (marvelously played by the late great Jerry Ito)
Honorable mention – believe it or not but for me it would be Jun Tazaki’s General in War of the Gargantuas. He is head of national security and there to protect the people, but when he ignores the wishes and pleas of the scientific community to save the good natured Sanda, he then became a villain in my book!