The Oxford Thesaurus An A-Z Dictionary of Synonyms - agent n.

1) representative, intermediary, go-between, proxy, emissary, delegate, spokesman, spokeswoman, spokesperson, deputy, substitute, surrogate, advocate, emissary, legate, envoy, factor: Our agent in Tokyo will look after the matter for you. 2) factor, agency, cause, means, force, instrument, power, vehicle, ingredient: The active agent in this cleaner is ammonia.