Mackay, John William (măkˈē) [key], 1831–1902, American financier, b. Dublin, Ireland. He immigrated to the United States in 1840. In 1859 he joined the rush to Nevada, where silver had been discovered. He and J. G. Fair, later joined by William Shoney O'Brien and J. C. Flood, acquired control of valuable silver mines, which yielded them great fortunes. With James Gordon Bennett he founded (1883) the Commercial Cable Company and laid two submarine cables to Europe. Later (1886) he organized the Postal Telegraph Cable Company.