Before Linux (the kernel) came along, GNU was known as an operating system, written from scratch to replace proprietary systems with a free clone of UNIX—that's why GNU is “not UNIX”. The effort was started by Richard Stallmann in 1984. It was only the kernel that was missing, when people began to use GNU with Linux in 1991.This was remembered by the early distributions, but nowadays most people think that Linus Torvalds wrote the complete OS (which was even claimed on kernel.org for a long time), and that Stallman is just a zealot who wants to steal his fame. This is not only false, but also bad for the free software movement: many people get a negative impression and never get confronted with the idea of Free Software—but all the more with the idea of Open Source! Open Source, however, is a term that was specifically invented to avoid the political issues associated with the term "Free Software".
The Philosophy of Free Software is not easy to explain. If you are interested in this topic, you should watch a speech of Richard Stallman. It's long, but interesting!The explanation Why Software Should Not Have Owners is also worth reading.