Rabbi Yitzchak bar Sheshet Perfet, also called Barfat and known by the acronym Rivash, was born in 5086 (1326) in Spain, in Barcelona according to some sources and in Valencia according to others. He was one of the great halachic authorities and judges of the period of the Rishonim and among the most prominent sages of fourteenth-century Spain.

In Barcelona he studied under Rabbi Peretz HaKohen and Rabbi Chasdai Crescas the Elder, but his principal teacher was the Ran, Rabbeinu Nissim of Gerona. Even during his teachers' lifetimes, questions reached him from distant communities, yet for many years he declined any rabbinic post and preferred to earn his living in trade. Together with the Ran and other leaders of the community he was imprisoned for five months on a false accusation before being found innocent.

Around 5140 (1380) he accepted the rabbinate of Zaragoza. Disputes within the community led him to leave for Calatayud, and he later settled in Valencia, where he served as rabbi and headed a yeshiva. The persecutions of 5151 (1391) forced him to flee Spain: after a stay in Miliana he settled in Algiers, where he was received with great honor and became rabbi of the community. A refugee who sought to lead the community turned against him, and the official appointment obtained for him from the authorities drew the opposition of the Rashbatz, Rabbi Shimon ben Tzemach Duran; the Rivash then withdrew from the rabbinate.

Only his responsa have survived: more than five hundred of them, first printed in Constantinople in 1546-1547. Rabbi Yosef Karo reports that his teacher Rabbi Yaakov Berav preferred them to those of other authorities, and he cites them extensively in the Beit Yosef; they underlie many rulings of the Shulchan Aruch. The Rivash also wrote liturgical poems and laments, including elegies for the destroyed community of Barcelona. He was cautious toward Kabbalah: in a well-known responsum (no. 157) he advises against engaging in it without having received it from a teacher.

He passed away in Algiers in 5168 (1408); many observe his hilloula on 2 Elul. His tomb, restored by the Algiers community in 1862, was a place of pilgrimage on the anniversary of his death until the departure of the Jews from Algeria. It was moved when the city expanded and now stands next to that of the Rashbatz, under a shared monument.