Complex sentence: He frequently quotes his teacher, Meir ben Baruch, and much of "the Mordechai" is written in support of the Tosafists, the last of whom were Mordechai's teachers.
Split into simpler sentences: He frequently quotes his teacher, Meir ben Baruch. Much of "the Mordechai" is written in support of the Tosafists, the last of whom were Mordechai's teachers.