The antonyms for the term "counter agent" vary depending on the context of its usage. In the context of espionage or intelligence, the antonym for counter agent would be "agent" or "spy." In a more general context, counter agent could be synonymous with "opposer" or "enemy," thus the antonym would be "ally" or "supporter." Additionally, if referring to a person tasked with countering the effects of a drug, the antonym could be "enabler" or "facilitator." The antonyms of counter agent will therefore depend on the context in which it is used, and the opposites will differ accordingly.