Sarah Mellon Scaife, often referred to as Sarah Scaife MacArthur, was an American heiress and philanthropist born into the prominent Mellon banking family. As the daughter of William Larimer Mellon and niece of industrialist Andrew Mellon, she inherited substantial wealth from the family's banking, oil, and industrial fortunes. In 1931, she married David W. Scaife, a Pittsburgh businessman, and together they established the Sarah Scaife Foundation in 1941, which became one of the earliest and most significant funders of conservative causes in the United States. The foundation supported institutions promoting free-market economics, anti-communism, and traditional values, influencing networks of conservative think tanks and policy organizations. Following her husband's death in 1962, she continued to oversee the foundation's operations until her own passing in 1965. Her philanthropy laid the groundwork for the Scaife family's enduring role in conservative funding, with her son, Richard Mellon Scaife, later expanding these efforts through additional family trusts. The Sarah Scaife Foundation provided major donations to organizations like the Center for Security Policy, contributing to networks of influence in national security and ideological advocacy. Her life exemplified the intersection of old money, family legacy, and political philanthropy, shaping conservative movements without direct personal involvement in politics.