Honorary citizen of the United States
A person of exceptional merit who is not a United States citizen may be declared an honorary citizen of the United States by an Act of Congress or by a proclamation issued by the U.S. president, pursuant to authorization granted by the U.S. Congress. Eight people have been so honored: six posthumously, and two, Sir Winston Churchill and Mother Teresa, during their lifetimes.
Source: Wikipedia — Honorary citizen of the United States (CC BY-SA 4.0)