A person who devises or engages in a counterplot; someone who schemes to prevent another's conspiracy.
From counterplot + -er (agent noun suffix). This compound noun emerged as a specific character type in espionage literature and political history from the 16th century onward.
Cardinal Richelieu in 17th-century France famously employed counterplotters—spies whose sole job was to discover and prevent plots against the king, making them perhaps history's first organized counterintelligence agents.
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