Beit Yosef Choshen Mishpat 14:1a

At this time, it is evident that the important people of a generation are called the “Great Court.” Thus Rabbenu Tam said that the greatest [sage or judge] of a generation has always been appointed as the chief [of the Great Court.] just as (according to Pesachim 66b) when the last children descended from the princeship and they appointed Hillel the next one [נשיא or prince] on account that he was greatest amongst them [the sages of his generation], therefore, it [his court] was called the “The Great Court”. As it is written, at the beginning of the chapter of Sanhedrin 32 regarding judgments of damages, Justice, justice you shall Pursue, (Deut 16:20) go after a good court, after Rabbi Eliezer to Lod, after Rabbi Yochanan son of Nori to Baror Chayil. Rabbi Matiya ben cheresh to Rome. (B. San 32b) From this we learn, even if [the court is] in Rome we call it “The Great Court” because there is none higher. And here ends his words. [Translation by Rabbi Rachael Bregman]