William Frederick Nast (1840–1893) was an American diplomat and entrepreneur. He was the third president of the Atchison, Topeka and Santa Fe Railway.
Nast was born in Cincinnati, Ohio, on June 14, 1840, the son of Methodist religious leader William Nast. From 1861 to 1865 he served at the American Consulate in Stuttgart, Germany. a daughter of pioneer St. Louis banker Louis Auguste Benoist. They had four children: Louis, Condé, Ethel, and Estelle.
While living in Europe, William Nast filed for several invention patents, including one for "improvements in the treatment of stable manure, and in the manufacture of paper" on July 6, 1876, awarded February 22, 1878, and one for "improvements in the manufacture of dextrine, sugar and the like, from cellulose and ligneous materials" on November 4, 1880, and , awarded on December 13, 1887.
He died in 1893, and was buried at Calvary Cemetery in St. Louis.