Parashas Bamidbar
וּנְשִׂיא֙ נְשִׂיאֵ֣י הַלֵּוִ֔י אֶלְעָזָ֖ר בֶּן־אַהֲרֹ֣ן הַכֹּהֵ֑ן פְּקֻדַּ֕ת שֹׁמְרֵ֖י מִשְׁמֶ֥רֶת הַקֹּֽדֶשׁ׃
The head chieftain of the Levites was Eleazar son of Aaron the priest, in charge of those attending to the duties of the sanctuary.
Torah Temimah points to R’ Yehoshua ben Levi / TT (verified).
ונשיא נשיאי הלוי אלעזר — ר׳ יהושע בן לוי אמר: אלעזר דוך דוכנים היה.
English: “The chief of the chiefs of Levi, Elazar” — R’ Yehoshua ben Levi said: Elazar was the officer of the officers.
Custom
Chazal describe Elazar as the head of all the Levitical chiefs.