Aaron ben Moses ben Asher lived in Tiberius during the first half of the 10th century. His family had been involved in creating and maintaining the Masorah for either five or six generations. Ben-Asher rapidly gained fame as the most authoritative of the Tiberias masoretes, and, even after his death, his name continued to hold respect.

In 989 CE, an unknown scribe of a former Prophets manuscript vouched for the care with which his copy was written by claimiing that he had vocalized and added the Masorah "from the books that were [vocalized] by Aaron ben Moses Ben-Asher."

RaMBaM, by accepting the views of Ben-Asher (though only in regard to open and closed sections), helped establish and spread his authority. Referring to a Bible manuscript then in Egypt, he wrote: "All relied on it, since it was corrected by Ben-Asher and was worked on and analyzed by him for many years, and was proofread many times in accordance with the masorah, and I based myself on this manuscript in the Sefer Torah that I wrote"

Since most Torah scribes today continue to rely on the writing rules of RaMBaM as their guide, the Masorah as established by Aaron Ben Moses Ben Asher was influential indeed.

His vocalization of the Bible is still, for all intents and purposes, the text Jews continue to use.

Moreover, Aaron ben Moses ben Asher was the first to take Hebrew grammar seriously. He was the first systematic Hebrew grammarian. His Sefer Dikdukei ha-Te'amim (Grammar of the Vocalizations) was an original collection of grammatical rules and masoretic information. Grammatical principles were not at that time considered worthy of independent study. The value of this work is that the grammatical rules presented by Ben-Asher reveal the linguistic background of vocalization for the first time. He had a tremendous influence on the world of Biblical grammar and scholarship.

From documents found in the Cairo Geniza, it appears that this most famous masorete (and, possibly, his family for generations) were also, incidentally, Karaites.

It should not be surprising to discover that many masoretes, so involved in the Masorah, held Karaite beliefs. After all, it was the Karaites who placed such absolute reliance on the Torah text. It would be natural that they would devote their lives to studying every aspect of it.

The surprising element was that being a Karaite didn't disqualify Aaron ben Moses ben Asher in the eyes of Rabbinic Jews (like RaMBaM).

With one exception:

It was known that Saadia Gaon had written against the Karaites. In his critiques, Saadia mentioned a "Ben Asher." Until recently, it never occurred to Jewish scholars to associate the "Ben Asher" of Saadia's diatribe with the famous Aaron ben Asher of Tiberius. After all, Aaron ben Asher was respected throughout the Jewish world. The Karaites were considered outsiders. It was unthinkable that traditional "normative" Jews would accept the work of a Karaite.

Recent research indicates, however, that it is probable that the subject of Saadia's attack was Aaron ben Moses ben Asher.

In his work Sefer Dikdukei ha Te'amim, Aaron ben Asher wrote, "The prophets... complete the Torah, are as the Torah, and we decide Law from them as we do from the Torah." That's pretty Karaitic. It also has forced scholars to re-evaluate the relationship between Jews and Karaites in the 10th century despite the writings of Saadia Gaon.

Sources: Gates to Jewish Heritage