Dies, Martin, Jr. (dĪz) [key], 1901–72, American political leader, b. Colorado, Tex. A lawyer, he represented Texas as a Democratic member of the U.S. House of Representatives (1931–45; 1951–59). He urged Congress to create what became the House Un-American Activities Committee and was its first chairman. The committee was notorious for its exposés of alleged Communist infiltration into U.S. business and government. Dies wrote The Trojan Horse of America (1940).