Judaism is not a centralised religion with a single head. Although some countries have a head rabbi for that country, in most places different communities have their own head rabbi. Often, a single city with a large Jewish population will have a different head rabbi for different groups. Israel has two head rabbis, one Ashkenazi and the other Sephardi, for example.
There is no head. Each community has its Rabbi(s).
There is no Hierarchy The Rabbi is the head of each synagogue then there is a cantor and the people.
Judaism is not a centralized religion with a "head Rabbi" or any single leader. Some countries have chief rabbis, but they are more like advisors for their specific communities. The United States does not have a chief rabbi.
There is no single head of Judaism. In classical times, there was the king, the Cohen Gadol (High Priest) and the head of the Sanhedrin (the greatest Torah scholar). Today, each Rabbi, greater or lesser, heads a particular community. The word 'Tzaddik' is a title meaning 'righteous'. Any person can become a tzaddik, they do not have to be a rabbi to do so.
Some area of Judaism. The rabbi could be the head of a synagogue, or a kosher-supervisor, or the dean of a Rabbinical college, or the person responsible for one or more of the many (other) facets of Judaism. Some rabbis are simply members of a synagogue and are otherwise "private citizens" within Judaism.
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The cantor
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Judaism.