Hassan al-Mustadi Ibn Yusuf al-Mustanjid (1142 – 30 March 1180) (Arabic: المستضيء بأمر الله) was the Abbasid Caliph in Baghdad from 1170 to 1180. Like his predecessor, he continued to occupy a more or less independent position, with a vizier and courtly surroundings, and supported by only a small force sufficient for an occasional local campaign. During his reign, Saladin ended the Fatimid caliphate, became the Sultan of Egypt and declared his allegiance to the Abbasids.
Benjamin of Tudela, who traveled to this area between 1160 and 1173, noted: "Two days from Akbara stands Bagdhad. The large metropolis of Calif Emir-al-Mumenin al Abassi Amir al-Mu'minin, of the family of their prophet, who is chief of the Mahometan religion. All Mahomatan kings acknowledge him, and he holds the same dignity over them which the Pope enjoys over the Christians. The palace of the Calif at Baghdad is three miles in extent. It contains a large park filled with all sorts of trees, both useful and ornamental, and all kinds of beasts, as well as a pond of water carried thither from the river Tigris; and whenever the Calif desires to enjoy himself and to sport and carouse, birds, beasts and fishes are prepared for him and for his courtiers, whom he invites to his palace. This great Abasside is extremely friendly towards the Jews, many of his officers being of that nation; he understands all languages, is well versed in Mosaic law, and reads and writes the Hebrew tongue. He enjoys nothing but what he earns by the labor of his own hands, and therefore manufactures coverlets, which he stamps with his seal, and which his officers sell in the public market..."
In 1180, Caliph Al-Mustadi died and was succeeded by his son Al-Nasir.