Though many people see "Linux" and think it refers to a single operating system, it in fact refers to an entire family of operating systems described as "Unix-like". What these operating systems have in common is that they were written in the Linux kernel. A kernel is the most central aspect of an operating system. It actually spans the gap between software implementations, or applications, and the work of processing data that is done by the physical hardware in a computer. The kernel is a very distinctive component of an operating system. Essentially, this means that several different types of computers and computing environments can correctly be referred to as being Linux systems.
Linux itself is famously known as being created by Linus Torvalds, though there were also thousands of other collaborators whose input was indispensible to the overall success of the project. As a matter of fact, the manner in which Linux came about, as an open-source collaborative project, is one of the keys to understanding its spirit and philosophy as an operating system. The term open-source means that the code of a piece of software is not hidden but actually freely viewable, sharable and malleable to all interested parties. This type of approach allows talented and creative programmers from all over the world to be able to contribute to a project simply because they are free to access and view code which is usually proprietary and secret within the realm of commercial software.
In 1991, Linus started off the massive collaborative effort by writing the original Linux kernel. However, we would be amiss not to acknowledge the shoulders of previous giants he stood upon while engaged in this creation. Linux was the next evolution in a series of projects that began with UNIX, an operating system written under the auspices of AT&T's Bell Laboratories by Ken Thompson in 1969. Through several new iterations and re-adaptations, and thanks to a loophole that required the company to license their creation, soon the software was making its rounds amongst inventive and forethoughtful programmers.
One such programmer, Richard Stallman, created the GNU project in the year 1983. The project's main impetus was to develop a complete software-suite that would be compatible with a UNIX system. However, due to various difficulties, the kernel and several other key elements of this software package were delayed or incomplete. Torvalds has been quote as saying that if this had not been the case, and if, in fact, the GNU package was complete and featured a working kernel, he would not have felt compelled to develop Linux's kernel.
Eventually, it was through careful and collaborative combinations of GNU, MINIX, another similar software project intended for education use, and the Linux Kernel itself that came to be the Linux we know and love today.