William Larimer Mellon Sr. (June 1, 1868 – October 9, 1949),[3][4] sometimes referred to as W. L., was an American businessman who was active in Republican Party politics.

[20][21] During the 1880s, William L. Mellon developed an interest in the burgeoning petroleum industry in Pennsylvania,[22] but he switched his business interests to the construction and operation of railway systems before the end of the decade when his nascent oil company was bought out by John D. Rockefeller's Standard Oil in 1895.

During the fall of 1924, his name was in the news frequently as he testified during United States Senate hearings about potential political corruption.

Known at the time as the Borah Committee hearings, these sessions were held to investigate expenditures of more than $3,451,000 that had allegedly been made by the Republican Party to influence voter opinions regarding various issues being debated at the federal level.

Ten years later, in 1949, Mellon donated six million dollars to establish the graduate school of industrial administration at the Carnegie Institute of Technology in Pittsburgh,[29] which is today the David A. Tepper School of Business at Carnegie Mellon University.

Its mission is to encourage both individual and corporate matching gift donations to support the school's operations.