Oathbreaker, generally speaking, is the title given to any individual who has gone back on his pledges, whether they be pledges of cultural, social, religious, or physical nature.
About
Oathbreakers are commonly former Paladins or Knights, but any creature who has reneged on a promise can be granted the title.
In Troverthian Culture, being labeled an Oathbreaker is a potentially lethal sentence, due to the prevalence of onomancy in the region, resulting in the reputation of the oathbreaker following a creature even in regions they have never visited before. The most common Oathbreakers found in the Troverth kingdom were Samurai who had given up on their lifestyle, or lost loyalty in their emporer.