Carly Fiorina, HP's chairperson, president and chief executive officer, called Hewlett a "great and gentle man." Others remembered him as a good natured, approachable person with a sharp intellect that allowed him to pick up quickly on new ideas and technologies.
Hewlett co-founded HP with his friend David Packard in 1939 while the men were students at California's Stanford University. Hewlett oversaw the company's expansion from its roots in testing and measurement equipment into new types of electronics equipment, including scientific calculators, computers and imaging products.
"Bill was a very down-to-earth, kind and thoughtful person. He was very curious and interested to learn about his employees," said Edward Barnholt, chief executive officer of Agilent Technologies, the testing and measurement division of HP that was spun out in 1999. Barnholt worked with Hewlett for 34 years at HP before leaving to lead Agilent.
One of Hewlett's proudest achievements was the management philosophy he developed at HP, Barnholt said. From the outset, both Hewlett and Packard, who died in 1996, promoted a flat management structure and an environment in which individual achievement was rewarded and employees felt valued.
"Both individuals had a strong belief in the potential of people, and that the manager's job was to create an environment that allowed people to achieve their potential," Barnholt said. "I think that idea was very different from the management philosophy that prevailed at the time. Management by objectives, management by wandering around -- a lot of these practices are commonplace around Silicon Valley today, more of the personal touch."
As Hewlett once put it: "We did not want to run a hire and fire operation, but rather a company based on a loyal and dedicated workforce." Packard wrote down the pair's management credo, which became known as the "HP Way".
Hewlett will also be remembered as a philanthropist. In 1966 his family established the William and Flora Hewlett Foundation, which has awarded grants worth millions of US dollars in the areas of education, environmental conservation, and US-Latin American relations. In 1994 he donated $US70 million to the Public Policy Institute of California, a non-profit research group that aims to improve public policy.
Hewlett was born May 13, 1913, in Ann Arbor, Michigan. He moved to California at age 3 when his father, who was a physician, joined the faculty at Stanford's medical school. Hewlett later enrolled at Stanford himself, where he befriended fellow engineering student Packard.
In 1939, at the urging of one of their professors, the young men founded HP using $US538 in personal funds. The company's first product was an audio oscillator, a precision device for conducting scientific measurements in fields like acoustics and oil exploration. The Walt Disney Company used eight of the products to help create the soundtrack for its musical cartoon movie "Fantasia".
Hewlett has most often been described as the scientific mind behind HP, while Packard supplied the business savvy. One often cited story from the late 1960s describes how Hewlett asked engineers at HP's Labs -- one of his favourite haunts -- to design a version of HP's desktop calculator that would fit in his shirt pocket. The result was one of the world's first handheld scientific calculators, introduced in 1972.
The garage in which the two men started HP has been made a California state historical landmark. Last year, HP bought the building, which it has used in advertising campaigns that try to highlight its no-frills, shirt-sleeved beginnings.
Hewlett was a US Army Signal Corps officer in World War II, and returned to HP in 1947 to become company vice president. He became HP president in 1964 and chief executive officer in 1969.
He remained president until his resignation from the job in 1977, and turned over the reigns as CEO the following year. He served as chairman of HP's executive committee until 1983, when he became vice chairman of the HP board of directors. In 1987, he was named director emeritus.
In the 1960s, when US President Lyndon Johnson was in office, Hewlett served on the President's General Advisory Committee on Foreign Assistance Programs and the President's Science Advisory Committee. In 1985 then-U.S. President Ronald Reagan awarded Hewlett the national medal for Science, the nation's highest scientific honour.
In his day, Hewlett also enjoyed skiing, mountain climbing, hunting and fishing.
He is survived by his second wife, Rosemary, as well as five children from his first marriage and five step children from his second marriage.