A 21-year-old computer science student in Helsinki bought his first PC in early 1991 and immediately hated the operating system it came with. So he sat down to write his own. On September 25, 1991 he posted a quiet message to a Usenet newsgroup announcing what he called "just a hobby, won't be big and professional like GNU." 35 years later that hobby runs every Android phone on Earth, every supercomputer on the TOP500 list, the entire backend of the internet, the International Space Station, and SpaceX's Falcon rockets. His name is Linus Torvalds. The hobby is called Linux. Here is the story, because the man who runs the most consequential codebase in human history almost no longer needs an introduction inside engineering and still walks the streets unrecognized everywhere else. Linus was born in Helsinki, Finland on December 28, 1969. He was named after Linus Pauling, the only person in history to win two unshared Nobel Prizes, in Chemistry and in Peace. He joked he might also be partly named after Linus van Pelt from the Peanuts cartoon. His family was unusual. Both parents were journalists. His grandfather was a statistician. Another grandfather was a poet. The family belonged to Finland's Swedish-speaking minority. There are fewer than 30 people in the world with the surname Torvalds, and according to Linus, they are all related. At 10 he started programming on his grandfather's Commodore VIC-20. By his teenage years he was writing his own assemblers, editors, and games. He served in the Finnish Army for his mandatory national service and rose to the rank of Second Lieutenant. Then he enrolled at the University of Helsinki to study computer science. In early 1991 he bought a personal computer with MS-DOS and disliked it intensely. He wanted UNIX, the operating system he had used at the university. UNIX cost thousands of dollars. He could not afford it. So he started writing his own. He posted the now-famous announcement to comp.os.minix in August 1991. He called the kernel Linux, a portmanteau of his name and MINIX. He released the source code under the GPL license. Anyone could download it, read it, modify it, and ship it for free. Within a year hundreds of developers around the world were sending him patches. Within five years Linux was running web servers. Within ten years it had taken over the supercomputer market. Within twenty years it was running on most of the internet. Today every Android phone on Earth runs the Linux kernel. Every Chromebook runs Linux. Most of AWS, Google Cloud, and Microsoft Azure runs Linux. Every Tesla runs Linux. Every SpaceX Falcon 9 and Dragon capsule runs Linux. The International Space Station runs Linux. Every supercomputer in the world's TOP500 list runs Linux. That was the first thing he built. In 2005 the proprietary version control system the Linux community had been using, BitKeeper, revoked its free license. Linus was furious. He sat down and wrote a replacement in 10 days. He called it Git. The first commit was on April 7, 2005. Today Git powers GitHub, GitLab, and the source control of every major software organization on Earth. Every line of code at OpenAI, Anthropic, Google, Meta, and Microsoft flows through Git. Every AI model on the planet is versioned with software a Finnish engineer wrote in less than two weeks. He won the 2012 Millennium Technology Prize, the equivalent of a Nobel Prize for engineering. He won the IEEE Computer Pioneer Award in 2014. He completed his master's degree from Helsinki along the way, with a thesis titled "Linux: A Portable Operating System." He moved to the United States, became a citizen, and now works from his home in Portland, Oregon, employed by the Linux Foundation. A Finnish student announced a hobby project on a message board in 1991. His code is now in every pocket on the planet. He still writes most of his important communication on the Linux kernel mailing list.