First of All, What is Linux?
You see, there is a contradiction on what Linux really is. We see that people refer Linux as an Operating System but on the other hand, some people say that Linux is a kernel. Well, let’s put it this way.
In fact, Linux is a kernel written and named by Linus Torvalds which you can take a look from https://www.kernel.org/. When you think about it, kernel is a useless thingy if there is no software using it since kernel manages hardware based on software inputs.
At this point, we have a cute kernel with us.
On the other hand, Richard Stallman initiated GNU Project, aiming to create a free Operating System with free tools. They were pretty succesful with the mission but there was one thing missing. A proper kernel to manipulate hardware by these tools.