Abu'l-Faraj Ya'qub ibn Yusuf ibn Killis (Arabic: يعقوب ابن كلس, romanized: Abu’l-Faraj Yaʿqūb ibn Yūsuf ibn Killis, Hebrew: יעקוב אבן כיליס), (930 in Baghdad – 991), commonly known simply by his patronymic surname as Ibn Killis, was a high-ranking official of the Ikhshidids who went on to serve as vizier under the Fatimids from 979 until his death in 991.
Ya'qub ibn Yusuf ibn Killis was born in Baghdad in 930 in a Jewish family. After his family moved to Syria he came to Egypt in 943 and entered the service of the Regent Kafur. As soon as he became the household and property administrator, he was in charge of the Egyptian state's finances. Despite converting to Islam in 967, he was imprisoned by Kafur's successors after losing their favor. He was able however to purchase his freedom and went to Ifriqiya, where he put himself at the service of the Fatimid Caliph al-Mu'izz.
After the Fatimid conquest of Egypt in 969, Ibn Killis returned to Egypt and was put in charge of the economy, where he was able to regularise the state finances. After the dismissal of Jawhar as-Siqilli in 979 Ya'qub ibn Killis was appointed vizier by al-Aziz, a position he held until his death in 991. He was a patron of culture and science.