He has never flown in a plane or used a computer, but thanks to the advances in transport and communications that have taken place during the course of his lifetime, Rabbi Yosef Shalom Elyashiv, who turned 100 this week, is the most influential rabbi in the world.
He has not held an official position for the past 35 years, never written a book or given a speech to a large audience and has no pupils of his own, and yet he has achieved an unrivalled degree of power over the Jewish Orthodox world. Rabbi Elyashiv could single-handedly resolve the issue of conversion, and he can block any resolution. Last week, he did just that when, on his orders, the new conversion bill, which would have given rabbis of towns the authority to perform conversions, potentially diluting the power of the chief rabbinate, was removed from the Knesset agenda.
He is the ultimate arbiter in matters of halachah, or Jewish religious law, not only in Jerusalem, the city he has not left in decades, but throughout the world.
For the past three decades he has held the title of Posek HaDor, the arbiter of the generation. This is a title that was never officially conferred on him but it reflects a consensus of the leading rabbis of that very generation and the realisation that there is one spiritual authority capable of shouldering the responsibility for the most serious rulings and serving as the last court of appeal on questions of halachah.
With the decline and then death of Rabbi Eliezer Shach eight years ago, he also became the most senior political authority for the "Lithuanian" stream of the ultra-Orthodox community, represented in the Knesset by the Degel Ha-Torah faction of United Torah Judaism. There are only two Degel MKs, but they have inordinate influence just by serving as Rabbi Elyashiv's parliamentary representatives.
His last few decades have been spent in the same 100 yards of space, between a tiny two-room flat on the edge of Meah Shearim in Jerusalem and the little shul where he has delivered a daily Talmud lesson for over 50 years. Most of his time is devoted to his own studies.
The rabbi's control over the religious-political establishment has never been stronger but he cannot go on forever. His followers must wish he would: he has no designated successor, no body of work that will continue after him, and no mechanism within the Charedi world of reaching major decisions in his absence.