John Denis Ryan (October 10, 1864 – February 11, 1933) was an American industrialist and copper mining magnate.

[3] He began selling lubricating oil in the western American states from a base in Denver, Colorado.

During World War I, Ryan took leave from Anaconda to work for the government and the American Red Cross.

[5] President Wilson appointed Ryan as new head of the Aircraft Production Board in April 1918, succeeding Howard Coffin.

Shortly after the war had ended in late 1918, Ryan resigned and returned to private business.

Under Percy Rockefeller, Ryan and Kelley, Anaconda acquired additional mining businesses outside the United States and by the 1920s, was expanding into new areas of activity which included manganese, zinc, aluminum, uranium and silver.

The prices, under the pressure of a "joint account" set up by Ryan and Rockefeller of nearly a million and a half shares of Anaconda Copper Company, fluctuated from $128 in December 1928 to $40 in March 1929.

As president of Montana Power, he fostered electrification of the Butte, Anaconda and Pacific Railway and electrical improvements in the mines.

Carrie Johnson, a historian, wrote a story about Ryan's rise to power which was published in Montana – The Magazine of Western History.