Tosafist and liturgical poet who suffered martyrdom at York, Eingland, in March, 1190, as has been proved by Grätz ("Gesch." 6:455). The Jews of York sought refuge in the fortress from the fury of the populace; and after offering a vain resistance for several days the most of them, on the advice of Yom-Ṭob ben Isaac, joined him in voluntary death.
Yom-Ṭob was a pupil of R. Tam, and was prominent as a tosafist, being frequently mentioned with the epithet "ha-Ḳodesh" (= "the Holy" or "the Martyr"). He also was a Biblical exegete and a liturgical poet. His best-known productions are OMNAM KEN, a hymn sung on the eve of the Day of Atonement, and a penitential prayer in fourteen stanzas. He wrote also an elegy beginning with the words "Yah tishpok" and lamenting the death of the Jews of Blois who perished in 1071.