Born in 1166 in Paris, France, his father Rabbi Isaac Treves was a rabbi in Paris, son of
Yom Tov of Falaise who was the son of
Judah ben Nathan (Rivan), and thus a descendant of
Rashi. In his early years, he learnt under
Isaac ben Samuel of
Dampierre and his son
Elhanan ben Isaac of Dampierre. He married a daughter of
Abraham ben Joseph of Orleans, who has been identified by Jacobs with Abraham fil Rabbi Joce, chief Jew in
London in 1186. In a list of that year associated with Abraham occurs the name of Leo Blund, whom Jacobs identifies with Judah ben Isaac. Sir Leon must have left
Paris in 1182, when all Jews were expelled from the French king's dominions; he did not return until 1198. According to Gross, however, he received his chief training at
Dampierre under
Samson of Sens,
Samson of Coucy,
Solomon of Dreux, and
Abraham ben Nathan of
Lunel. Shortly after 1198 he returned to Paris and founded an important school of tosafists, in which were trained, among others,
Jehiel ben Joseph (Sir Leon's successor),
Isaac ben Moses of Vienna (author of
Or Zarua),
Samuel ben Solomon of Falaise (Sir Morel of Falaise), and
Moses of Coucy. ==Teachings==