1055 - 1130 ISAAC BEN ASHER HALEVI (The Rivah) (Germany)
Called the "Father of the German Tosafists". He studied briefly under Rashi, and was the only outstanding German teacher to survive the First Crusade. Upon his death there was no one of standing to take his place and the schools of Worms and the Rhineland were surpassed by those further south. It was said of him that he went over his lessons four times before he would teach them.