William Rockefeller (1841-1922), American financier, was a cofounder of Standard Oil and the younger brother of John D. Rockefeller.

Rockefeller was born in Richford, New York. In 1853 his family moved to Strongville, Ohio.

In 1865, he entered the oil business by starting a refinery. In 1867, his brother's company, Rockefeller & Andrews, absorbed this refinery, and in 1870, the company became Standard Oil.

William Rockefeller had success at manipulating stock, and served as the company's New York representative until 1911, when Standard Oil of New Jersey was dissolved. He also had interests in copper, railways, and public utilities. He built up the National City Bank of New York,and his son William Goodsell Rockefeller and Elsie Stillman,daughter of National City Bank president James Stillman,were the parents of James Stillman Rockefeller.