The Spanish Jewish scholar and theologian Moses Maimonides wrote the metaphysical book in the 12th century.
The least I can do to do justice to the guy is to read carefully that Wiki entry.
He comes to mind because we visited his synagogue in Cairo a couple of weeks ago, often referred to as the Maimonides Synagogue.
There are not enough Jews in Cairo to maintain an active synagogue. Photos of the interior are not permitted. I don't know why. It is a simple place.