Mr Gates rushed to Georgia to be with his mentor, Dr Henry Edward Roberts, last Friday, when he heard he was ill, Dr Roberts’ son David said.
Dr Roberts, 68, died on Thursday after battling pneumonia.
He was often credited with kick-starting the modern computer era.
The designer’s build-it- yourself kit concentrated thousands of dollars worth of computer capability in an affordable package and inspired Mr Gates and his childhood friend Paul Allen to come up with Microsoft in 1975 after they saw an article about the MITS Altair 8800 in Popular Electronics magazine.
Ex-military man Dr Roberts, better known as Ed Roberts, later went on to be a farmer and a physician, but continued to keep up with computer advances. He recently told Gates he hoped to work with new, nanotechnology-enhanced machines, according to his son.
“He did think it was pretty neat, some of the stuff they’re doing with the processors,” said David Roberts.
“Ed was willing to take a chance on us — two young guys interested in computers long before they were commonplace — and we have always been grateful to him,” Mr Gates and Allen said in a joint statement.
“The day our first untested software worked on his Altair was the start of a lot of great things. We will always have many fond memories of working with Ed.”
Born in Miami in 1941, Roberts spent time in the US Air Force and earned an electrical engineering degree from Oklahoma State University in 1968.
He later put his interest in technology into a business making calculators but when large firms like Texas Instruments began cornering the business, he soon found himself in debt, his son said.
Meanwhile, he was gaining an interest in computers. “He came up with the idea that you could have one of these computers of your own,” David Roberts said. “Basically, he did it to try to get out of debt.”
Dr Roberts himself would later describe the effort as an “almost megalomaniac kind of scheme” that he pursued out of youthful ambition.
“But at that time, you know, we just lacked the benefits of age and experience,” he said on a TV programme called Triumph Of The Nerds, in 1996. “We didn’t know we couldn’t do it.”
His son described him as a tinkerer who surveyed his friends before building his personal computer.
“My assumption was that there were a bunch of nuts out there like me that would like to have a computer,” Roberts told the Atlanta Journal-Constitution in 1997.
“To engineers and electronics people, it’s the ultimate gadget.”