Linus Torvalds
Born in Helsinki in 1969, Linus Torvalds began Linux in 1991 as a free, Unix-like kernel for his home PC while still a university student. He announced it on a Usenet newsgroup as a hobby project he figured would never be 'big and professional' — an estimate that aged poorly, as Linux now runs the majority of the world's servers, every Android phone, and essentially all of the top supercomputers.
In 2005 he wrote Git, the distributed version-control system, in roughly two weeks. The kernel project had been relying on a proprietary tool called BitKeeper, and when free access to it was withdrawn, Torvalds built his own replacement. Git went on to become the dominant version-control system in software development.
Decades on, he still coordinates Linux kernel development, known equally for his sharp technical judgment and his famously blunt feedback on the kernel mailing list.