The title of King (S."Aran" Q."Aran", E."Haran") was the most common title of a head of a realm, which, in the ancient days of Middle-Earth, was the preeminent form of government. Originating as the title of greater chieftains of the Elves during their Great Journey, the title originally meant Great One, a political figure whose authority surpassed that of a mere clan-leader, and was derived from his character, skill, charisma, leadership and - in later times - blood and destiny. As a result, all Elvish monarchies had started as electivr, charismatic monarchies but eventually transformed into hereditary monarchies, and were absolute in political authority, with power concentrated in the hands of (generally aged males, but others under females and youths were documented) members of single great families or clans. The Feanorians, for example, were led by Fëanor's sons after his death as King of the Noldor, and they became kings in their own right, the eldest son bearing the title of High-King; this however proved to be chiefly titular, as the lesser Kings, while they formally acknowledged the High-Kingship, paid its bearer little heed and generally maintained autonomy.
Men quickly imitated the concept, replacing their traditional chieftaincies, although they applied it in different ways. Their early monarchies were generally elective, as with the chieftaincies, and those of great merit and age (it was rather rare for a youth to become a monarch amongst men) for their lords. The Númenóreans were the first to replicate the ways of the Elves; their kings, who officially bore the title "High King," descended from the line of Elros Tar-Minyatur, and they held reletively absolute authority over their people and vassals. Their offshoots amongst the colonies of Númenor organized in various ways, though generally related to those of their ancestors; the Black Númenóreans always maintained a great lord amongst themselves, though in some realms, Umbar, for one, were ruled by what was considered a council of rival lords, acting in a sort of confederate monarchy. The northwestern Elendili in Gondor and Arnor at maintained faithful the Númenórean traditions of powerful monarchy, under a High-King from the House of Elendil the Tall; however after Elendil's death the North kingdom and South kingdom devolved into independent realms, each with a king of its own; nonetheless, they came still from the line of the Lords of Andúnië and thus were remote descendants of Elros Half-Elven, and they maintained the traditions and ways of the ancients in governance. Aragorn Elessar was the first true High-King to rule a Reunited Kingdom after more then three thousand years, and under him the Elendili state was restored in near-perfect form.
The Middle-Men and Men of Darkness in Middle-Earth applied very exotic concepts of kingship, from elective monarchy based on charisma to hereditary kingship derived from great deeds of old. Vidugavia was a Northman chieftain who claimed the title of King as the cap to long success and authority as politician and warlord. Another case is that of the Kings of the Bardings; Bard Bowman was the first of his line who took the title of King, his ancestors the rulers of Dale, being merely Lords and nobles. However, Bard was the only monarch his line to be elected by acclamation to kingship; after his death, his eldest son inherited the title, transforming the elective monarchy of his young kingdom into an official hereditary monarchy. Similarly, Eorl the Young was considered the first King of the Rohirrim; his forefathers had possessed only the title of Chieftain and authority only as the head of the leading family of the Éothéod. Eorl was elected king by his people, but his sons inherited the position, founding the hereditary monarchy of Rohan.
Equivalents of King in the languages of Middle-Earth:
- Ar- - royal prefix in Quenya. Used as a title by the Númenóreans.
- Aran - Sindarin and Quenya word for King. Used by the Noldor, Sindar, Nandor and Dúnedain.
- Ashdurbuk - title of the Orc-Ruler of Gundabad and all the Orcs of the North; the High-Chief of the North and King of the Orcs.
- Atârn - Ky'târi
- Autarb - Harûze title of a local King or Petty King.
- Bôm - Balchoth title for their eldest or King.
- Brenhin - a Dunlending Hill-Chief or Petty-King.
- Cyning - the Rohirric or Éothéodan word for King.
- Great Goblin (or Durba-Hai)- an extremely powerfulGoblin-chieftain, used chiefly in Goblin-Town, and sometimes in Moria.
- Hûrdriak or Hûr - originally the High-King or High-Chief of the Asdriags, later just the title of a local Lord under Balchoth Rule.
- Hûz of Amôv - originally a personal name, later title and appellation for a Great King or leader of a coalition of tribes among the Rhûn-Easterlings.
- Jí - Mûmakanin title for a King or sacred-King.
- Kân - a "Khan" or "Khagan" of the Rhun-Easterlings.
- Kank - the Warlord and later King or Rúartar.
- Kataj - Ioriags, Kykuria.
- Khûdriag, Khûrdirag or Khûr - title of the Kings of Khand.
- Khurdriag-Ata - a Variag god-king or sacred King.
- Konung - Rhovanian word for king among the Bardings.
- Kralyî - title for the king of Rây or Bôzisha-Mîraz.
- Lôke-Kân - title of the Dragon-Ruler of the Golden Army of Rhûn.
- Morachd - title of the King of the Mountains among the Mountainmen or Oathbreakers.
- Mûl - title of the King of Wômawas Drûs.
- Rhi - title of a local lord or petty King in Minhiriath or Enedhwaith.
- Rí - title of the King among the Hillmen.
- Sey - a wise overlord of the Ahar-Easterlings.
- Szem - title of a King among the Shrel and later Easterlings of Rhun.
- Tar- - royal prefix in Quenya. Used as a title by the Númenóreans and High-Elves.
- Tári - Quenya word for Queen.
- Tarb or Taryb - in Near-Harad a lesser local Lord, in Greater harad a City-King or the Greatest King of Sirayn.
- Taskral or Taskrel - in Near-Harad a powerful city-king or Stone-King.
- Théoden - Rohirric personal name and word for king.
- Ulfar - Vothrig.
- Uzbad - a dwarven lord or King under the Mountain.