The father of fathers of... / The greatest of all...
Figuratively: the greatest of all; the main or original source of something.
("Three primary sources of impurity — how so? A man who touches a corpse becomes the father of fathers of impurity; a sword that touches the man becomes a father of impurity." — Midrash Agadah (Buber), Numbers 19)
Translation
Expression (Hebrew)
אֲבִי אָבוֹת הַ...
Definition (Hebrew)
בְּהַשְׁאָלָה: הַגָּדוֹל מִכֻּלָּם. הָרָאשִׁי אוֹ הַמָּקוֹר לַכֹּל.
("שְׁלשָׁה אָבוֹת הַטֻּמְאָה, הָא כֵּיצַד? נָגַע אָדָם בְּמֵת נַעֲשָׂה אֲבִי אֲבוֹת הַטֻּמְאָה, נֶגַע חָרֵב בָּאָדָם נַעֲשָׂה אַב הַטֻּמְאָה" - מִדְרַשׁ אַגָּדָה (בּוּבֶּר) בַּמִּדְבָּר, יט)