The image of James K. Polk (1790-1849), the eleventh president of the United States (1845-1849), appears on the 11-cent value of the 1938 Presidential Series. Polk's likeness on the stamp was derived from a medal struck by the U.S. Mint. This ultramarine stamp was printed only as a sheet stamp and was issued on September 8, 1938.
Interestingly, the first two stamps produced by the United States were issued during Polk's presidency (1847), but this 11-cent denomination was the first to feature his image.
While this 11-cent stamp can be found in use with other stamps, solo usages are somewhat scarce. A single 11-cent stamp would have paid the international surface rate for up to three ounces (five cents for the first ounce and three cents for each of the next two ounces) in effect October 1, 1907, through October 31, 1953, as well as the combination air/surface/air rate to Europe (five cents for the international surface rate plus three cents for domestic air service and a three-cent supplement for air carriage within Europe), in effect November 23, 1934, through the beginning of World War II.