Ed Roberts

Mr Gates rushed to Georgia to be with his mentor, Dr Henry Edward Roberts, last Friday, when he heard he was ill, Dr Roberts's son David said today. Dr Roberts, 68, died on Thursday.

Dr Roberts 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 Mr 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.

Dr Roberts died in a Macon hospital after a long bout of pneumonia, his family said.

Neither Mr Gates nor Mr Allen was immediately available for comment yesterday.

Born in Miami in 1941, Dr 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 – at the time hulking machines available almost exclusively at universities.

"He came up with the idea that you could have one of these computers on your own," David Roberts said, adding his father had only expected to sell a few units.

"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, eh, the benefits of age and experience," he said on a TV programme called Triumph of The Nerds, shown 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," Dr Roberts told the Atlanta Journal-Constitution in 1997. "To engineers and electronics people, it's the ultimate gadget."

The Altair was nothing like the ultra slim laptops of today. Operated by switches and with no display screen, it looked like little more than a metal box covered in blinking red lights.

"In the early days it was pretty useless. People just bought it thinking that it would be neat to build a computer," Mr Gates said in a video history interview with the Smithsonian Institution.

Dr Roberts founded Micro Instrumentation and Telemetry Systems, which sold the kits. A young Mr Gates and Mr Allen would later found their fledgling Microsoft firm in Albuquerque, New Mexico, where MITS was based, and provide a computer language that helped hobbyists programme and operate the Altair.

The men fell out after Mr Gates and Mr Allen began selling versions of BASIC – or Beginners All-purpose Symbolic Instruction Code – created for Altair to competitors, according to the 2003 book, Leaders of The Information Age.

But David Roberts said they had since overcome their differences, and his father had remained an influence in both their lives.

He sold his company in 1977 and retired to a life of vegetable farming in rural Georgia before going to medical school and getting a degree in 1986.

He worked as an internist, seeing as many as 22 patients a day, his son said. But he never lost his interest in modern technology, even asking about Apple's highly anticipated iPad from his sick bed.

"He was interested to see one," said David Roberts, who called his father "a true renaissance man".