William Reddington Hewlett (May 20, 1913 – January 12, 2001) was an engineer and the co-founder, with David Packard, of the Hewlett-Packard Company (HP). He was born in Ann Arbor, Michigan, only to move with his family to Oak Brook, Illinois when he was two. However, in less than year, his family moved once again to San Francisco when he was three, to where he spent the rest of his life in the San Francisco Bay Area. He attended Lowell High School and was accepted at Stanford University as a favor to his late father, Albion Walter Hewlett, a former faculty member at the Stanford Medical School who had died of a brain tumor in 1925.

Hewlett received his Bachelor's degree from Stanford University in 1934, an MS degree in electrical engineering from MIT in 1936, and the degree of Electrical Engineer from Stanford in 1939. He joined the Kappa Sigma fraternity during his time at Stanford.

Hewlett attended classes taught by Fred Terman at Stanford and became acquainted with David Packard during his undergraduate work at Stanford. He and Packard began discussing forming a company in August 1937, and founded Hewlett-Packard Company as a partnership on January 1, 1939. A flip of a coin decided the ordering of their names. The company incorporated in 1947 and tendered an initial public offering in 1957. Hewlett was president of the Institute of Radio Engineers in 1954. Also in 1939 he married Flora Lamson, and the couple eventually had five children: Eleanor, Walter, James, William and Mary. There are 12 grandchildren.

He was President of HP from 1964 to 1977, and served as CEO from 1968 to 1978, when he was succeeded by John A. Young. He remained chairman of the executive committee until 1983, and then served as vice chairman of the board until 1987.

In 1966, he and his wife founded the William and Flora Hewlett Foundation. Flora Hewlett died in 1977. In 1978, Hewlett married Rosemary Bradford.

He died of heart failure at Portola Valley, California, on January 12, 2001, and was interred at Los Gatos Memorial Park, San Jose, California.