Marcus Daly (December 5, c. 1840s – November 12, 1900) was an Irish-born American businessman known as one of the four "Copper Kings" of Butte, Montana, United States.

He sold newspapers and worked his way to California in time to join the gold rush on what was to become Virginia City, Nevada, and the fabulously rich silver diggings now known as the Comstock Lode, in 1860.

Daly originally came to Butte in August 1876 to look at a mine, the Alice, as an agent for the Walker brothers of Salt Lake City.

He envisioned an ore body several thousand feet deep, some veins of almost pure copper that would be worth hundreds of millions of dollars.

[4]: 50–52 In 1886, Daly bought property in Hamilton, Montana, building a summer residence and creating the Bitterroot Stock Farm, a 22,000 acre ranch and horse breeding facility.

In order to bring water to the agricultural fields, Daly invested in several ditch companies to build irrigation canals throughout the valley.

Shortly thereafter he became involved in the timber industry in the Bitterroot Valley, purchasing acres of timberland and building sawmills to provide fuel for the smelters in Anaconda.

[4]: 64, 67  Shortly before this time, Thomas Edison had developed the light bulb and built a city block in New York to show off what electricity could do.

[8] He built a smelter to handle the ore, and by the late 1880s, had become a millionaire several times over, and owner of the Anaconda Mining and Reduction Company.

[8] Daly's lumber and investment interests in the Bitterroot Valley spurred the creation of a rail line by the Northern Pacific Railway in Hamilton.

[9] In 1894, Daly spearheaded an energetic but unsuccessful campaign to have Anaconda designated as Montana's state capital, but lost out to Helena, which was supported by William Andrews Clark.

A number of his horses were successful, which some speculators attributed to the elevation and climate of Hamilton, and others to the rich feed produced by the valley.

[11] He also arranged the breeding of the great Sysonby, ranked number 30 in the top 100 U.S. thoroughbred champions of the 20th Century by Blood-Horse magazine, though Daly died before the horse was born.

[12] Following his death, New York's Madison Square Garden hosted a dispersal sale for the Bitterroot thoroughbred stud, beginning on January 31, 1901; 185 horses were sold the first day for $405,525.

In 1980 the Berkeley Pit, the Clark Fork River and the smelter outside the town of Anaconda, MT were declared federal Superfund sites by the US EPA.