An agent who has the freedom to eliminate any threat he perceives in any manner he sees fit.
Usually such agents are covered by "
plausible deniability" - the agent is told what his job is, but not through the normal
chain of command, so that the orders are not recorded. This way, if the agent is captured or killed, the
government who sent the agent can claim that he was a rogue agent, acting without official orders or permission.