If you haven't read it, Torvalds' book is pretty interesting. He's a fairly blunt writer of prose - alas, no Hemingway - but has a good voice and his slightly-cynical Finnish humour comes through clearly. Doesn't have the massive ego that you might have expected, either - he knows he's one of the planet's biggest nerds.
Essentially, his somewhat geeky summer project was to implement the POSIX parts of Minix as a learning exercise, and basically locked himself in his room till he'd done it. Photocopied the spec sheet, and was 'ticking off' all the calls he'd got working. He was dual-booting with Minix for a while, which is why the filesystem layout is the same, but at one point managed to break his Minix boot, and Linux had to become self-hosting.
Fair play to him - took him a few months to produce the OS kernel that the whole GNU team couldn't manage in a decade. Perfect is the enemy of good. Open-sourcing 'something that works' was all that was needed for everyone else to add in all the bits they needed as well, and the rest is history.