An alabarch was a traditionally Jewish official in Alexandra during the Hellenistic and Roman periods, seemingly responsible for taxation and especially customs at the harbor.
The following alabarchs are known by name:
"Alabarch" is the a Latinization of a Greek title, Ἀλαβάρχης, often described as a corruption of Arabarch (Ἀραβάρχης), meaning "Arab leader".
Professor Samuel Krauss in the 1906 Jewish Encyclopedia suggests that the alabarch was the leader of the Jews in Alexandria, and would have been called "ethnarch" by gentiles including Strabo.
The title of an official who stood at the head of the Jewish population of Alexandria during the Grecian period. [...] Strabo (quoted by Josephus, "Ant." xiv. 7, § 2), who was in Egypt about 24 B.C., calls the governor of the Jews "ethnarch" (ἐθνάρχης), and remarks that he ruled over the Jews as over an autonomous community (Ως ἄν πōλιτείας ἄρχων αὐτōτελōῦς). If the term as used by Strabo is correct, then the Alabarch must have been known among the heathen as ethnarch; so that one would surmise that the term ἀλαβάρχης was used only by the Jews. Strabo's ethnarch is usually identified with the Alabarch, without further question; but Franz is of the opinion ("C. I. G." iii. 291a) that the Alabarch was only a subordinate functionary of the ethnarch. Grätz ("Monatsschrift," xxx. 206) considers the alabarchs to be descendants of the priest Onias, who emigrated to Egypt; and he includes the generals Hilkias and Ananias among the alabarchs, though authority for this is lacking.
He considers the "Arab" etymology unlikely for a term applying to a leader of only the Jewish community and proposes the alternative "alaba" referring to ink from tax records:
The trend of modern opinion is to connect it with the Greek term for ink, ἄλαβα (alaba), taking ink in the sense of writing (scriptura), which, in those days, was a token for tax (vectigal). Such a derivation would imply that the Alabarch was a farmer of taxes, certainly from the time of the Ptolemies; and, judging by inscriptions which give a similar title to an office of the Thebaid in Egypt, he must also have collected the toll on animals passing through the country.