In ancient times, the Klingon Empire was ruled by dynastic emperors. The reign of the last Klingon emperor ended in the mid-21st century, after which the chancellor, leader of the Klingon High Council, assumed the leadership of the Empire. Following the "return" of Kahless, the role of Klingon emperor was reinstated as a ceremonial position, to strengthen the hearts of the Klingon people. (TNG: "Rightful Heir")
Background
Dialogue in TNG: "Sins of the Father" written before the canon structure of Klingon culture had been fully conceptualised by the writing staff implies that there was a Klingon Emperor at least as late as 2364. At one point Kahlest insists to Jean-Luc Picard that Mogh "was loyal to the Emperor" at the time of the Khitomer Massacre.
See also
List of known Klingon emperors
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