Jawdhar, surnamed al-Ustadh, 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 was ranked immediately after the caliph and his designated heir. The accession of al-Mansur was probably due to Jawdhar's machinations, and he was placed in charge of keeping the new caliph's relatives under house arrest. He enjoyed close relations with the Kalbid emirs of Sicily, which enabled him to engage in profitable commerce with the island. Jawdhar accompanied al-Mu'izz during the migration of the court from Ifriqiya to Egypt, but died on the way at Barqa. 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.

A eunuch is a male who has been castrated. Throughout history, castration often served a specific social function. The earliest records for intentional castration to produce eunuchs are from the Sumerian city of Lagash in the 2nd millennium BCE. Over the millennia since, they have performed a wide variety of functions in many different cultures: courtiers or equivalent domestics, for espionage or clandestine operations, castrato singers, concubines or sexual partners, religious specialists, soldiers, royal guards, government officials, and guardians of women or harem servants.