Linux is a clone of the Unix, which was the leading operating system developed in early 1970's.
Linux fits in the movement started by the Free Software Foundation (FSF), which is a nonprofit with a worldwide mission to promote computer user freedom.
Apart of FSF is the GNU (GNU is Not Unix) Project with a mission to provide a complete operating system which is Free Software:
in the 1980's many GNU free utilities were already launched and in 1992 Linus Torvalds added Linux kernel to GNU that made GNU system complete: it was possible to install Linux along with GNU utilities as an actual operating system.
To make installation possible, in those days, some early distributions were provided: Yggdrasil and Slackware were amongst these early distributions.