The story of Linux begins with UNIX, an operating system developed at AT&T Bell Labs in the 1970s. UNIX is written in the C language making it uniquely portable amongst competing operating systems, which were typically closely tied to the hardware for which they were written. It quickly gained popularity in research and academic settings, as well as amongst programmers who were attracted to its modularity. Over time it was modified and forked (that is, people modified it, and those modifications served as the basis for other systems) such that at present there are many different variants of UNIX. However, UNIX is now both a trademark and a specification, owned by an industry consortium called the Open Group. Only software that has been certified by the Open Group may call itself UNIX.
Linux started in 1991 as a hobby project of Linus Torvalds, a Finnish-born computer scientist studying at the University of Helsinki. Frustrated by the licensing of MINIX, a UNIX-like operating system designed for educational use, and its creator’s desire not to make it a full operating system, Linus decided to create his own OS kernel.
From this humble beginning, Linux has grown to be the dominant operating system on the Internet, and arguably the most important computer program of any kind. Despite adopting all the requirements of the UNIX specification, Linux has not been certified, so Linux really isn’t UNIX! It’s just… UNIX-like.