A high king is a king who holds a position of seniority over a group of other kings, without the title of Emperor. Similar titles include Great King and King of Kings. The high kings of history usually ruled over lands of cultural unity; thus high kings differentiate from emperors who control culturally different lands, and feudal monarchs, where underlings assume lesser positions. High kings can be chosen by lesser rulers through elections, or be put into power by force through conquest of weaker kingdoms.
In history and literature, high kings may be found where there is a high degree of cultural unity, along with sufficient political fragmentation that the high king's subordinates style themselves, kings. In this respect, high kingships frequently differ from empires, which are culturally as well as politically heterogeneous, as well as from feudal monarchies, where the subordinate rulers take lesser titles (such as duke or count) and maybe, at least in theory, subject to appointment and dismissal by the sovereign.
In this model, a high king might be chosen from among a group of kings in his personal capacity, for instance by election or on the basis of genealogical superiority. Alternatively, the high kingship might be attached to the kingship of one of the constituent kingdoms, either permanently or when one kingdom is able to assert supremacy over the others. The high king's authority over other kings is usually limited, and in some high kingships his duties are largely ceremonial or restricted to occasions such as war that create a need for a unified command structure.
Rulers who have been termed "high king" (by their contemporaries or by modern observers) include:
The Yang di-Pertuan Agong (literally Supreme Lord) in Malaysia could probably be seen as a "high king", as he is elected from among nine Malay rulers of the states (seven Sultans, a Raja, and a Yang di-Pertuan Besar-literally Great Lord) by the Conference of Rulers (through informal agreement, on a rotational basis). In practice, however, the term "high king" is rarely applied to the Yang di-Pertuan Agong, rather "King".
"Taewang", meaning "greatest of kings", was used by the later rulers of the Korean kingdom of Koguryo (and Silla, albeit to a rarer extent) to rank themselves as equals to the Chinese Emperors or to express suzerainty over surrounding states, particularly during the Three Kingdoms Era. "Daewang" ("great king") was used by rulers of other kingdoms and subsequent dynasties, including Baekje, whose king assumed the style of "Daewang Pyeha" ("His Imperial Majesty the Great King") by the reign of King Mu (600-640 AD) at the latest. However, after the Mongol Invasions of Korea, these rulers remained technically subordinate to the Mongol Empire and later China until King Gojong declared the Korean Empire in 1897 and assumed the title of "Hwangje", or Emperor (the Korean rendition of the Chinese "huang di").
Originally, the rulers of Wa (倭), an ancient name of Japan, was known as the "Grand King of Yamato" (大和大王, Yamato-ōkimi) or the "Kings of Wa" (倭国王, Wakoku-ō) prior to the 7th century. It was later changed to become the Emperor of Japan (天皇, Tennō).
The title "King of Kings" also expresses much the same concept as "high king" – it was used at various times by the Emperor of Persia (shahanshah) and the Emperor of Ethiopia. Similarly, the Imperial Mongolian title Khagan is sometimes translated as Khan of Kahns.