Complex sentence: Noel Field (January 23,1904--September 12,1970) was an American citizen who, while employed at the U.S. Department of State in the 1930s, was a Soviet spy.
Split into simpler sentences: Noel Field (January 23,1904--September 12,1970) was an American citizen. While employed at the U.S. Department of State in the 1930s, he was a Soviet spy.