Rabbi Ahron ben Yosef HaKohen (Also know as Ahron Sargado) served as Gaon of Pumbeditha for a duration of 16 years from 4704 (943 CE) until his passing in 4719 (959 CE), he carried the title ראש ישיבת גאון יעקב.
A student of Rav Mevasser Gaon, the Even Ezra in his Torah commentary quotes a Rav Ahron who some attribute to the said Rav Ahron. A reliable description of Rav Ahron can be gleanded from the responsa of Rav Hai Gaon, where he records Rav Ahron HaKohen in a favorable light;
We all remember the many Shabbatot at the residence of our master Rav Ahron Gaon where we would pray at his home and he would sit from prayer time until the evening
The Rambam in his Moreh Nevuchim work (Arabic version, end of vol.1), Rav Ahron is referred to as having authored several treatises to combat the false belief of evolution.
Rav Ahron apparently was not viewed favorable by Rav Sherira Gaon (as opposed to Rav Hai Gaon cited prior), as is evident by Rav Sherira’s description of Rav Ahron not being worth of his Gaon status (see Igrot Rav Sherira Gaon, ch.130). Other’s reconcile Rav Sherira’s words as not being written with the intent to imply that Rav Ahron was not a Talmid Chochom, as is evident by his statement that Rav Ahron was superior in Torah instruction to Rav Nechemya.
Four of Rav Ahron HaKohen’s halachic responses are currently known, the first of which involved an individual who had sworn that his daughter not marry Shimon, the individual then came before the bet-din of Rav Ahron (Teshuvot HaGeonim ch. 37), the remaining Halachic responsa of Rav Ahron can be viewed in the Chamuda Genuza work (available online at hebrewbooks.org).
Rav Ahron is said to have collaborated with Rav Shmuel ben Chofni HaKohen Gaon in his Torah commentary compilation (see introduction of Rabbi A. Greenbaum to Rav Shmuel’s ben Chofni’s Torah commentary, p. 24).
See more Kohen greats who made a significant contribution to Torah instruction and Halacha literature