Little was known of Aaron until Adolf Neubauer discovered, among the manuscript collection of Abraham Firkovich in Saint Petersburg, important fragments in Arabic of the Mushtamil "The Comprehensive", a Hebrew grammar consisting of eight books.
He was acknowledged by the Rabbanites as one of the principal representatives of Karaitic learning and as a great authority on grammar and exegesis.
He is quoted by Abraham ibn Ezra in the preface to his Moznayim as "the sage of Jerusalem, not known to me by name, who wrote eight books on grammar, as precious as sapphire."
Judah ibn Balaam likewise mentions "the grammarian of the Holy City"; and Jonah ibn Janah in his Riqmah relates that Jacob de Leon brought him from Jerusalem "the copy of a book by an author who lived there, but whose name he refrains from mentioning," because, as Bacher surmises, he was a Karaite.
Abu al-Faraj occasionally cites from the Hebrew-Arabic dictionary compiled by David ben Abraham al-Fasi.