Thane
Thane in reality is an archaic name for a leader from the Anglo-Saxon sphere of the Bronze Age and Iron Age worlds, heavily associated with people like the Celts, Vikings and basically anyone from before Europe had proper kings and queens. As such, the concept sometimes pops up in fantasy gaming as either a social rank or even something with mechanics behind it.
Dragon Magazine #323 offered the Thane up as a Fighter Variant Class for Dungeons & Dragons 3rd Edition, but unlike the Janissary that would debut 11 issues later, there actually is some mechanical basis to this one. These thanes are characterized as the elite protectors of clans and tribal chieftains; bodyguards, companions of rulers and commanders of warbands, often having the equivalent of noble blood themselves. They have the same weapon and armor proficiencies as regular fighters, but their class skills are Climb, Craft, Diplomacy, Handle Animal, Jump, Ride and Swim. There are three new feats they can take as bonus feats, but they're availble to anyone, and they have a single unique class feature; Thane's Vow. This is kind of a watered-down Paladin oath, with a touch of Samurai; basically, the Thane must declare a single character to be their lord and master, and must serve that chosen master to death. If their master is killed, they are obligated to avenge their death or die trying, which DMs are advised to treat as the equivalent of a Geas or Quest spell (except it can't be dispelled); the Thane suffers a -4 penalty on all Charisma skills until they succeed in avenging their master's death, and even then this only frees them up to swear loyalty to a new master, which is when the penalty finally disappears.