Hasdai rendered important services to the caliph by his treatment of an embassy headed by John of Gorze, sent to Córdoba in 956 by Otto I. The caliph, fearing that the letter of the German emperor might contain matter derogatory to Islam, commissioned Hasdai to open the negotiations with the envoys. Hasdai, who soon perceived that the letter could not be delivered to the caliph in its present form, persuaded the envoys to send for another letter which should contain no objectionable matter. John of Gorze said that he had "never seen a man of such subtle intellect as the Jew Hasdeu".