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Rav Avraham Zacuto (5212/1452–c. 5275/1515) was a rishon of Sefarad known across the world for his mastery of astronomy, and the author of Sefer Yuchasin. Born in Salamanca in Castile, he learned Torah — Gemara, halachah, and Kabbalah — from his principal rebbi, Rav Yitzchak Aboab, and studied astronomy at the university there.

His great astronomical work, the HaChibbur haGadol, was written in Hebrew and completed in 5238/1478; it set out detailed tables charting the courses of the sun, moon, and planets. Translated by his talmid Yosef Vizinho and spread under the Latin name Almanach Perpetuum, it changed the course of ocean navigation: Zacuto fashioned an astrolabe of copper in place of wood, letting seamen fix the position of the sun far more accurately. His tables and instruments were used by Vasco da Gama, whom he himself prepared for the voyage to India, and by Christopher Columbus. King John II of Portugal named him royal astronomer and consulted him on the sea route to India, which he encouraged; he continued in that post under Manuel I.

When Manuel I forced the Jews of Portugal to accept baptism and barred them from leaving, the rishon was among the few who escaped without abandoning his faith, though he and his son were twice taken captive on the way. He reached Tunis, where he wrote Sefer Yuchasin, a history of Klal Yisrael and its chachamim from the creation down to his own day, together with the chain of the tradition of Torah. In 5273/1513 he came up to Yerushalayim, and there, in the yeshiva of Rav Yitzchak HaKohen Shulal, he composed his calendar tables in Lashon HaKodesh for the first time and lived out his final years.