Trust, but verify was a signature phrase adopted and made famous by U.S. president Ronald Reagan. Reagan frequently used it when discussing U.S. relations with the Soviet Union. Reagan rightly presented it as a translation of the Russian proverb “doveryai, no proveryai” (Russian: Доверяй, но проверяй). Soviet revolutionary Vladmir Lenin also frequently used the phrase.
After Reagan used the phrase at the signing of the INF Treaty, his counterpart Mikhail Gorbachev responded: “You repeat that at every meeting,” to which Reagan answered “I like it.” (source: Wikipedia)