William Reddington Hewlett (May 20, 1913 - January 12, 2001) was the co-founder, with David Packard, of the Hewlett-Packard Company (HP). He was born in Ann Arbor, Michigan but moved to San Francisco at the age of 3 years. He attended Lowell High School and was accepted at Stanford University as a favor to his late father, Albion Walter Hewlett, who had died prematurely of a brain tumor in 1925.

Hewlett received his Bachelor's degree from Stanford University in 1934, an SM degree in EECS (course 6) from MIT in 1936, and the degree of Electrical Engineer from Stanford in 1939.

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 of 1937, and formally incorporated Hewlett-Packard Company on January 1, 1939. In 1939, he also married Flora Lamson, and the couple eventually had five children: Eleanor, Walter, James, William and Mary.

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, and in 1978. Hewlett married Rosemary Bradford.

In 1995 he received the Lemelson-MIT Prize Lifetime Achievement Award.