R. Hasdai b. Abraham ibn Crescas (d. 1412?), originated from Barcelona, where his activities as a merchant and communal leader can be traced back to 1367. In that year he was imprisoned, together with R. Nissim Gerondi, his teacher, and R. Isaac b. Sheshet, on a trumped-up charge of desecrating the Host, but was later released. Crescas wrote poetry, and in 1370 participated in a competition between the Hebrew poets of Barcelona and those of Gerona. He was among the delegates of the Catalonian Jewish community who negotiated with the king of Aragon for a renewal and extension of Jewish privileges in 1383. With the accession of John I (1387), Crescas became closely associated with the court of Aragon, and was accorded the title of member of the royal household (familiaris, de casa del senyor rey). In 1387 Crescas was empowered by royal decree to exercise the juridical powers available in Jewish law in order to enforce a ban of excommunication. Shortly afterward he settled in Saragossa, where he served as rabbi in place of R. Isaac b. Sheshet, who had taken up residence in Valencia. In 1390 John I permitted Crescas to prosecute informers against Jews and to impose punishment on them in accordance with the community's privileges. Soon after, the queen appointed Crescas as judge of all cases concerning informers in the Jewish communities throughout Aragon, but there is no documentary evidence of such an appointment. A son of Crescas suffered a martyr's death in Barcelona in the anti-Jewish riots of 1391. The queen and Crescas had written from Saragossa to the highest officials of Barcelona, asking them to give protection to Crescas' relatives, but their letters came too late to avert the tragedy. In Saragossa, which was the seat of the royal court, Crescas himself was safe from attack and collected funds from the Jewish communities in Aragon to pay for their defense. He prepared a chronicle of the massacres in the form of a letter to the Avignon community dated October 19, 1391 (published as an appendix to Ibn Verga, Shevet Yehudah, ed. by M. Wiener, 1855); its terse Hebrew bears theological allusions: The desolated centers of Jewish piety and learning become Jerusalem, and his son, "my only son, a bridegroom, a lamb without blemish," becomes Isaac. In 1393 Crescas, in conjunction with two representatives of the Saragossa and Calatayud communities, was authorized by the crown to select Jewish individuals and families from the communities of the kingdom with a view to their resettlement in Barcelona and Valencia, and to raise contributions from all the Jewish communities for the reconstruction of Jewish quarters in these cities. A document of 1396 shows that Crescas was actively engaged during this period in the general rehabilitation of Spanish Jewry. He also made efforts to reform the system of communal representation in Saragossa, and in 1396 framed regulations (no longer extant) for the community, aimed at strengthening the powers of its administrators. Certain modifications were introduced to them in 1399 by Queen Violante, who extended the responsibility of the administrators and allowed the lower classes a greater share in the representation. However, she continued to entrust Crescas with great authority in constitutional matters. He also helped to effect similar charges in neighboring communities where necessary. His influence was not confined to Aragon. Before 1391 he and R. Isaac b. Sheshet were approached for advice with regard to the succession of the chief rabbinate of France. Later his opinion was solicited by R. Joseph Orabuena, chief rabbi of Navarre, in a suit concerning one Judah Levi of Estella. In 1401 Crescas spent several weeks in Pamplona, perhaps to discuss with King Charles III problems regarding the Jewish population of the kingdom. A document from Olite, the royal residence in Navarre, acknowledges the receipt of 40 florins from the king, and bears the signature of Crescas in Hebrew and Spanish. He is not known to have engaged in any public duties during the last decade of his life, which he apparently devoted exclusively to his literary activities. After the martyrdom of his son he received permission in 1393 from the king of Aragon to marry a second wife, since his first wife was unable to have any more children. He died at Saragossa.

ספר אור ה' הוא החלק השני מספרו "נר א'להים". החלק הראשון, כעין השלמה לספר המצוות לרמב"ם ונקרא בשם "נר מצוה", לא יצא לפועל. בהקדמתו כאן כותב המחבר: "ולהיות החלק הזה (השני) יסוד ועמוד החלק האחר (נר מצוה), ראוי שיקדם לו בסתר [צ"ל: בסדר]". אך בחתימת הספר הוא כותב: נשלם המאמר (הרביעי) מהחלק הזה הראשון המכונה באור י"י ". דף [2,א]: שיר "על שש ועשרים הקדמות להרמב"ן [צ"ל: להרמב"ם, בפתיחת החלק השני מספרו מורה הנבוכים], הביאם המחבר". השיר פותח: בלי תכלית וכן רבים ועלות. שם המחבר בראש הבית השמיני: אני יצחק (אוצר השירה והפיוט, ב, עמ' 32, מס' 718). רוסט, קטלוג הרוזנטליאנה, עמ' 273, משער שהמחבר הוא ר' יצחק אלחכים. על הספר ועל מחברו, עי': ראובן מרגליות, ציונים ביבליוגראפיים, ארשת, א, תשי"ט, עמ' 418, מס' 1144; שמחה בונם אורבאך, עמודי המחשבה הישראלית, חלק שלישי, משנתו הפילוסופית של רבי חסדאי קרשקש, ירושלים תשכ"א; אליעזר שבייד, הפילוסופיה הדתית של ר' חסדאי קרשקש, ירושלים תשל"א.