From Karen Armstrong’s A History of God: The 4,000-Year Quest of Judaism, Christianity and Islam:

there is no objective view of “God”: each generation has to create the image of God that works for it.  The same is true of atheism.  The statement “I do not believe in God” has meant something slightly different at each period of history.  The people who have been dubbed “atheists” over the years have always denied a particular conception of the divine.  Is the “God” who is rejected by atheists today, the God of the patriarchs, the God of the prophets, the God of the philosophers, the God of the mystics or the God of the eighteenth-century-deists?  All these deities have been venerated as the God of the Bible and the Koran by Jews, Christians, and Muslims at various points of their history.  … [These deities] are very different from one another.  Atheism has often been a transitional state: this Jews, Christians, and Muslims were all called “atheists” by their pagan contemporaries because they had adopted a revolutionary notion of divinity and transcendence.  Is modern atheism a similar denial of a “God” which is no longer adequate to the problems of our time?