Jawdhar (Arabic: جوذر‎, before 909 – March 973), surnamed al-Ustadh (Arabic: الأستاذ‎, lit. 'the Master'), was a eunuch slave who served the Fatimid caliphs al-Qa'im, al-Mansur, and al-Mu'izz as chamberlain and de facto chief minister until his death. He was an extremely powerful figure in the Fatimid court, and the accession of al-Mansur was probably due to his machinations. His collected documents and letters were published after his death by his secretary as the Sirat al-Ustadh Jawdhar, and form one of the main historical sources for the governance of the Fatimid state in the period.