A computer science professor in Monterey, California wrote the operating system that ran every personal computer on Earth in the late 1970s. When IBM came looking for an OS for the machine that would define the next forty years of computing, a series of miscommunications, a disputed meeting, and a $40 pricing decision handed the deal to a 25-year-old in Seattle named Bill Gates instead. The professor died at 52 in a bar in Monterey. The 25-year-old became the richest person in the world. His name was Gary Kildall. Here is the story, because the most consequential missed deal in the history of technology is still argued about by everyone who was in the room. Gary was born on May 19, 1942 in Seattle, Washington. His father was a navigation instructor for merchant sailors. He studied at the University of Washington and earned a bachelor's in mathematics, a master's in computer science, and eventually a PhD in computer science. He became a professor at the Naval Postgraduate School in Monterey, California. While teaching there in the early 1970s he created something nobody else had built. An operating system for microcomputers. Before CP/M, every computer required its own custom-made software. CP/M abstracted the hardware away. Write the software once and it ran on any machine running CP/M. He invented the concept of the BIOS, the hardware abstraction layer that lives on today in UEFI firmware inside every computer you have ever used. He founded Digital Research Inc. with his wife Dorothy McEwen. By 1979 CP/M was the industry standard. It ran on the MITS Altair, the IMSAI 8080, the Osborne 1, and most of the early personal computers. DRI was generating $5 million a year in royalties. Microsoft at the time was a smaller company focused on programming languages. In early 1980 IBM started planning a personal computer. They needed an operating system. IBM went to Microsoft first. Bill Gates told them he did not have an operating system, but that they should go talk to Gary Kildall in Monterey because Gary did. Gates called Gary while the IBM executives were still in his office. He could not say who was coming because of a nondisclosure agreement. He told Gary to treat them well because they were important people. What happened next depends on who tells the story. In the popular version, Gary went flying in his plane and missed the meeting entirely. His children have said publicly that this is a myth. Multiple sources, including Kildall himself, have said he was back in his office that same afternoon. The real issue was not a missing CEO. It was a combination of factors. Dorothy reportedly refused to sign IBM's aggressive nondisclosure agreement without legal review. Gary and IBM disagreed on deal structure. IBM wanted to buy the OS outright. Gary wanted royalties. The tight timeline IBM demanded for a 16-bit version of CP/M added friction. The meeting fell apart. IBM went back to Microsoft. Gates acquired a product called QDOS, the Quick and Dirty Operating System, from a Seattle programmer named Tim Paterson for $50,000. Microsoft renamed it MS-DOS and licensed it to IBM. When DRI engineers finally got their hands on an IBM PC, they saw striking similarities between MS-DOS and CP/M. Gary was furious. He believed his work had been copied. IBM eventually agreed to sell CP/M alongside MS-DOS on the IBM PC. But CP/M was priced at $240. MS-DOS was priced at $40. The market chose the cheaper option. The rest is the history of Microsoft. Gary sold DRI to Novell in 1991 for roughly $120 million. He co-hosted a PBS television show called Computer Chronicles from 1983 to 1990. He launched KnowledgeSet, which produced the first CD-ROM encyclopedia. He kept inventing. But friends say the endless comparisons to Gates gnawed at him. On the night of July 8, 1994, Gary walked into a bar in Monterey. He hit his head. The circumstances are disputed. He declined treatment and was discharged from the hospital twice. Three days later he died from a cerebral hemorrhage. He was 52. A professor who invented the personal computer operating system lost the deal that built the largest fortune in technology. He died in the same town where he wrote the code.