Moses was the author of the book of Genesis, as well as the following 3 books of the Bible (The 4 books are known as the Torah.)
What about the first 11 chapters of Genesis? I can see the argument for Moses being the first to write the rest of Genesis (after the tower of Babel), but I believe the first 11 chapters were already recorded before Moses, and Moses included them into Genesis. Or perhaps Moses rewrote the account and then put it into Genesis.
And actually, it’s the first five books in the Pentateuch.
Genesis
Exodus
Leviticus
Numbers
Deuteronomy.