High King (Dwarves)

A High King, as the dwarves use the title, refers to a paramount ruler or over-king who has secured the fealty of multiple other rulers who themselves hold royal rank. The domain of such a ruler can thus be understood as a union or confederation of kingdoms bound together by the mutual loyalty of their kings to their common overlord, the High King. 
Humans often conflate this position with that of an emperor (or an emperor by another name, such as the Kirdan Tash-Teshivan, "King of Kings"), but for the dwarves, High Kingship is properly attained by alliance-building and diplomatic maneuvering, not conquest. A High King gains his position via reciprocal oaths, marriage alliances, inter-clan pacts, and above all, lawful dynastic seniority. Subjugating other kingdoms and turning their rulers into vassals by force makes one a tyrant and scarcely better than a manling or an orc (which is not to say it is unheard-of in dwarven history). 
The most prominent dwarven realm ruled by a High King is Kuzulkadrin, a huge state which dominates most of Rhydain's mountainous regions. In their typically ignorant way, humans often call it a "dwarven empire" and refer to its High King as the "emperor of the dwerrow" or similar such misnomers.