(ca. 1250-1327)
(Known called the Rosh). Ben Jechiel was known as a codifier of laws and leader of Jewish communities in Germany and Spain.

He was educated by his father and uncle, who were both well known and highly respected thinkers. He spent some time in France, where he met Rabbi Meir of Rothenburg. When Meir was imprisoned and held hostage, Aszer took over as chief rabbi of the Ashkenazim (i.e., the Jews of Germany and France). He worked on rebuilding the Jewish communities after the pogroms of 1298, and tried to free Meir. Because his own life was in danger, however, he fled Germany in 1303.

A year later, he arrived in Spain, where he became rabbi of a large Community in Toledo. Although he lived and died in poverty there, he was widely respected for his wisdom. He was often asked for advice, and he was even supported at the royal court because of the important influence he had on the Spanish Jews.

Asher took part in a dispute about the role and use of the study of philosophy. He believed that the ban on studying philosophy before the age of twenty-five that had been imposed by Salomon ben Abraham Adret was too lenient. In his opinion, the study of philosophy should be banned altogether. In the end, he supported Adret, but noted that this was not to say that he supported the philosophy behind his teachings.

Asher was involved in all aspects of rabbinical instruction. He sometimes spoke out against customs prevailing in Spain, which he considered to be the result of Christian influences. These included, for example, a law that allowed women to receive inheritance in the same proportion as men, the guarantee that the oldest sons receive all the property, and the requirement that a man grant a divorce to his wife if she has stated she no longer wants him as a spouse. Asher left over 1,200 "responses", i.e., answers to legal questions.