Quote:

Franta said:
from The Brave and the Bold # 28: "Starro the Conqueror!"

first appearance of the JLA

however their "origin" would later be reveiled.



So the Appellaxians would be considered the first JLA villains.

Or (if you include pre-Crisis stories that are no longer in continuity and were probably really contrived in the first place) the first villain would be Commander Blanx.