The Chancellor of the Klingon High Council was the Klingon head of government and the de facto head of the Klingon Empire. The chancellor replaced the emperor as the ruler of the Empire in the mid-21st century. The chancellor was protected at all times by the Yan-Isleth. (DS9: "Apocalypse Rising") However, many chancellors such as Gowron and Martok were known to take command of Klingon Defense Force vessels and lead attacks personally; Gowron commanded the IKS Bortas as Chancellor and Martok led Klingon forces in the Battle of Cardassia. (TNG: "Redemption" ; DS9: "What You Leave Behind")