Thane

Thane is an honorary title bestowed upon clan leaders, nobility, or royalty in dwarvish and vrykul societies.

Thanes in the Warcraft Universe
In Warcraft III: Reign of Chaos, the mountain kings are honorary thanes, although not true kings.

In World of Warcraft, thanes — explained by a Wildhammer NPC in Aerie Peak — are individual leaders of the many dwarf clans (much like pandaren Shodo-pan) while all still hailing to the High Thane, the king.

A thane rules each Wildhammer clan, and the mightiest thane rules Aerie Peak.

The High Thanes in WoW include King Magni Bronzebeard of the Bronzebeard Dwarves, High Thane Falstad Wildhammer of the Aerie Peak Dwarves, and Emperor Dagran Thaurissan — a descendant of Sorcerer-Thane Thaurissan — of the Dark Iron dwarves.

Lore
The Mountain Kings, or 'Thanes' as they are known in Khaz Modan, are the mightiest dwarven warriors under the mountain.

Ironforge dwarves also call mountain kings "thanes," an honorary title that respects the mighty warriors' prowess and strength. This moniker also recalls the day when most, if not all, mountain kings, truly were kings of the mountains, leading the dwarf clans in the deep caves. In modern times, Ironforge has a single king - but many mountain kings are nobles or other honorary personages, the scions of families whose names and deeds echo through the generations.

Wildhammer

 * Falstad Wildhammer 
 * Thane Yoregar - Wildhammer Stronghold, presumably under Kurdran Wildhammer

Dark Iron

 * Iron Thane Burningeye
 * Iron Thane Shadowforge
 * Sorcerer-thane Thaurissan
 * Thane Angerforge
 * Thane Corehammer
 * Thane Ironstar

Vrykul

 * Dragonflayer Thane - Wyrmskull Village
 * Halfdan the Ice-Hearted 
 * High Thane Jorfus - Unknown holdings, presumably in Icecrown
 * Overthane Balargarde 
 * Thane Banahogg - Unknown holdings in Jotunheim
 * Thane Illskar - Presumably The Underhalls in Jotunheim, possibly under Thane Ufrang
 * Thane Torvald Eriksson - Voldrune
 * Thane Ufrang the Mighty - Presumably Jotunheim

Iron dwarves

 * Iron Thane Argrum - Thor Modan
 * Iron Thane Furyhammer 

Unknown

 * Thane Korth'azz - Most death knights of note have some kind of title, thane being a dwarven one, it is unknown what he was in life