Career
He studied in Paris, Berlin, Brussels, and New York City. From 1918 to 1919 he was director of the Juarez Hospital, Mexico City, and the following year he was appointed director of the Mexican Army Medical School.
An accomplished linguist as well as a surgeon, Castillo NájeraNajera was called into the diplomatic service, and from 1922 to 1924 he was minister to China. For the next two years he studied in Europe. From 1927 to 1935 he was successively minister to Belgium, Holland, Sweden, France, and Austria. His longest appointment was as Mexican ambassador to the United States from 1935 to 1945, after which he returned to Mexico to become minister of foreign affairs. In 1945 he was Mexican delegate to the United Nations Conference on International Organization and in 1947 was briefly president of the UN Security Council.