Baruch de Spinoza (1632–77) was the son of a prominent merchant in Amsterdam's Portuguese-Jewish community. He was also among the more gifted students in its school. But something happened around his twenty-third year – whether it was sudden or gradual, we do not know – that led to the harshest excommunication ever proclaimed by the leaders of the Amsterdam Sephardim. The result was Spinoza's departure from the community – indeed, from Judaism entirely. He would go on to become one of the most important and famous philosophers of all time, and certainly the most radical and controversial of his own.

The young man's transformation (if that's what it was) from ordinary Jewish boy – living, to all appearances, a perfectly normal orthodox life and remarkable perhaps only for his intelligence – to iconoclastic philosopher is, unfortunately, hidden from us, possibly forever. We have only the cherem document, full of oaths and maledictions, that was composed by the community's governors. There is so little surviving material, so little that is known for certain about the details of Spinoza's life, particularly before 1661 (when his extant correspondence begins), that we can only speculate on his emotional and intellectual development and on the more mundane matters that fill out a person's existence. But what a rich field for speculation it is, particularly given the fascination of its subject.

Metaphysical and moral philosopher, political and religious thinker, biblical exegete, social critic, grinder of lenses, failed merchant, Dutch intellectual, Jewish heretic.