His family was prominent for learning and piety, his father Yechiel was a Talmudist, and one of his ancestors was Rabbi Eliezer ben Nathan (the RaABaN).

Asher had eight sons, the most prominent of whom were Jacob (author of the Arba'ah Turim) and Judah.

In 1286, King Rudolf I had instituted a new persecution of the Jews, and the great teacher of the Rosh, Rabbi Meir of Rothenburg, left Germany but was captured and imprisoned.

He was, however, forced to emigrate (in all likelihood, a victim of blackmail by the government, aimed at acquiring his fortune).

Rabbenu Asher's son Judah testified to the fact that he died in poverty.

The Rosh was known for his independent legal reasoning: "We must not be guided in our decisions by the admiration of great men, and in the event of a law not being clearly stated in the Talmud, we are not bound to accept it, even if it be based on the works of the Geonim."

He said that "none that go unto her may return"—in fact, he thanked God for having saved him from its influence, and boasted of possessing no knowledge outside the Torah.

This work was so important in Jewish law that Yosef Karo included the Rosh together with Maimonides and Isaac Alfasi as one of the three major poskim (decisors) considered in determining the final ruling in his Shulchan Arukh.