Yochanan ben Zakkai was the youngest and most distinguished disciple of Rabbi Hillel. He has been called the "father of wisdom and the father of generations (of scholars)" because he ensured the continuation of Jewish scholarship after Jerusalem fell to Rome in 70 C.E.
According to tradition, ben Zakkai was a pacifist in Jerusalem in 68 C.E. when the city was under siege by General Vespasian. Jerusalem was controlled by the Zealots, people who would rather die than surrender to Rome (these are the same people who controlled Masada). Ben Zakkai urged surrender, but the Zealots would not hear of it, so ben Zakkai faked his own death and had his disciples smuggle him out of Jerusalem in a coffin. They carried the coffin to Vespasian's tent, where ben Zakkai emerged from the coffin. He told Vespasian that he had had a vision (some would say, a shrewd political insight) that Vespasian would soon be emperor, and he asked Vespasian to set aside a place in Yavneh (near modern Rehovot) where he could start a small school and study Torah in peace. Vespasian promised that if the prophesy came true, he would grant ben Zakkai's request. Vespasian became Emperor within a year, and kept his word, allowing the school to be established after the war was over. The school ben Zakkai established at Yavneh became the center of Jewish learning for centuries and replaced Jerusalem as the seat of the Sanhedrin.
Sources: Judaism 101