No person "made up" the Quran. The Quran came down to Muhammad, peace be upon him, from Almighty God (Allah) by way of the angel Gabriel (Jibril in Arabic) and then it was memorized by him and he then in turn, would teach it orally to his companions.
The word "Quran" actually means the "Recitation" (spoken words). How do you "write sounds" recited sounds? - You actually only write what you hear and represent it with pen and ink on paper. Actually people can only write down words they hear of the "Quran" (Recital) as Muhammad, peace be upon him, recited it to them. The actual tone, pitch and sound are not really captured on paper.
When we have the Quran in written, book form it is usually referred to as 'scripture' ('mus-haf' in Arabic), although it is still Quran to us. So, while it is of course, possible to write down in book form, what we hear in some form or another, the main point is that Muhammad, peace be upon him, did not make up, fabricated or invent the words in the Quran. And there would be no way he could, as he was illerate and unable to read or write.
