What is "jawdhar"

Jawdhar, surnamed al-Ustadh, was a eunuch slave who served the Fatimid caliphs al-Qa'im (r. 934–946), al-Mansur (r. 946–953), and al-Mu'izz (r. 953–975) as chamberlain and chief minister until his death in 973. 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 one of his assistants as the Sirat al-Ustadh Jawdhar, and form one of the main historical sources for the governance of the Fatimid state in the period.