Rabbeinu Tam רבינו תם
head of the Tosafist school, Rashi's grandson
Rabbeinu Yaakov ben Meir, called «Tam» — «whole», as Scripture says of the patriarch Jacob — was Rashi's grandson through his mother and lived at Ramerupt in Champagne. He was wealthy, dealt in wine and in money, and maintained a large academy.
The Tosafist school he led changed how the Talmud is read. Rashi explained; the Tosafists compared. They would take a line here and a contradicting line two hundred folios away and demand an account of how both are true. From this grew all later Jewish legal reasoning — and the printed Talmud page, with Rashi on one side of the text and Tosafot on the other.
He disagreed with Rashi himself, respectfully and firmly; the dispute over the order of the passages in tefillin is famous, and «Rabbeinu Tam tefillin» are still worn by the scrupulous.
He was the acknowledged head of French and German Jewry, convening synods on divorce, informers and taxes. During the Second Crusade a mob broke into his house and wounded him five times; a passing knight saved him.