William Andrews Clark, Sr. was born in 1839 in Connellsville, Pennsylvania, and later lived in Iowa, where he taught school and studied law at Iowa Wesleyan College. During the Montana gold rush in the 1860s, he headed west where he first tried placer mining, and then chose to become a trader, provisioning miners across the state. He later opened a bank in Deer Lodge, Montana and made a fortune through reposessing mining claims when their owners defaulted on their bank loans. As he accumulated more mining holdings in Montana, particularly in Butte, he chose to enroll for a year of study at the Columbia University School of Mines. In addition to operating mines and smelters, Clark also diversified into railroads (including the San Pedro, Los Angeles, and Salt Lake Railroad), newspapers, and lumber, in addition to the Los Alamitos Sugar Corporation in Los Angeles and United Verde copper mine in Arizona. Clark served one term as a US Senator from Montana from 1901-1907, though the bribery scheme that bought him his seat colored much of his time in office. After leaving the Senate, Clark largely lived in New York City, where he accumulated a large collection of French art.

Clark's first wife, Katherine Stauffer, was also born in Connellsville, Pennsylvania, and after the births of their seven children, lived the majority of the rest of her life in France. She died in 1893. Clark's second wife, Anna Eugenia La Chapelle (1878-1963) had been a teenager in Butte when she met Clark, and he paid for her to study music in Europe. Their two daughters, Andree (1902-1919) and Huguette (1906-2011), were both born in Europe and largely raised in New York City.

Clark Sr. died in New York City in 1925.