Which American is famous for saying, "Trust, but verify"?

Trust, but verify is a translation of a Russian proverb. It became very well known when it was used by President Ronald Reagan in the context of nuclear disarmament in 1984.

Suzanne Massie, a writer in Russia, met with President Ronald Reagan many times between 1984 and 1987. She taught him the Russian proverb, "Доверяй, но проверяй" {Doveryai, no proveryai} (trust, but verify) advising him that "The Russians like to talk in proverbs. It would be nice of you to know a few. You are an actor – you can learn them very quickly." The proverb was adopted as a signature phrase by Reagan, who subsequently used it frequently when discussing U.S. relations with the Soviet Union.

After Reagan used the phrase to emphasize "the extensive verification procedures that would enable both sides to monitor compliance with the treaty" (INF Treaty), his counterpart General Secretary Mikhail Gorbachev at the signing of the treaty on December 8,1987 responded: "You repeat that at every meeting," to which Reagan answered "I like it." But, while Reagan quoted Russian proverbs, Mr. Gorbachev was fond of quoting Ralph Waldo Emerson.