If I recall correctly, it was written by Linus Torvalds a long time ago. I haven't found yet when it originally appeared, but it was probably the pre-Bitkeeper days; I found a discussion about it dated from the last century.

There were many edits to it, by several people; its more recent story can be seen on the kernel git repository. Of course, if Linus disagreed with an edit, it wouldn't go in, so in a way it's still his document.