Av Beit Din in the context of "Joshua ben Hananiah"

The Sanhedrin (Hebrew and Middle Aramaic סַנְהֶדְרִין, a loanword from Koine Greek: Συνέδριον, romanized: synedrion, 'assembly,' 'sitting together,' hence 'assembly' or 'council') was a Jewish legislative and judicial assembly of either 23 or 70 elders, existing at both a local and central level in the ancient land of Israel.

There were two classes of Rabbinite courts called sanhedrins: Greater and Lesser. A lesser Sanhedrin of 23 judges was appointed to sit as a tribunal in each city. There was only one Great Sanhedrin of 70 judges, which, among other roles, acted as a supreme court, taking appeals from cases that lesser courts decided. In general usage, the Sanhedrin without qualifier usually refers to the Great Sanhedrin, which was presided over by the Nasi, who functioned as its head or representing president, and was a member of the court; the Av Beit Din or the chief of the court, who was second to the Nasi and 69 general members.

Jonathan Henry Sacks, Baron Sacks (8 March 1948 – 7 November 2020) was an English Orthodox rabbi, philosopher, theologian, and author. Sacks served as the Chief Rabbi of the United Hebrew Congregations of the Commonwealth from 1991 to 2013. As the spiritual head of the United Synagogue, the largest synagogue body in the United Kingdom, he was the Chief Rabbi of those Orthodox synagogues but was not recognized as the religious authority for the Haredi Union of Orthodox Hebrew Congregations or for the progressive movements such as Conservative, Reform, and Liberal Judaism. As Chief Rabbi, he formally carried the title of Av Beit Din (head) of the London Beth Din. At the time of his death, he was the Chief Rabbi Emeritus.

After stepping down as Chief Rabbi, in addition to his international travelling and speaking engagements and prolific writing, Sacks served as the Ingeborg and Ira Rennert Global Distinguished Professor of Judaic Thought at New York University and as the Kressel and Ephrat Family University Professor of Jewish Thought at Yeshiva University. He was also appointed Professor of Law, Ethics, and the Bible at King's College London. He won the Templeton Prize (awarded for work affirming life's spiritual dimension) in 2016. He was also a Senior Fellow to the Raoul Wallenberg Centre for Human Rights.