One of my favorite characters I’ve played in an RPG was a goblin who believed he was an Archmage, and that his magic was powered by turnips. (He had no magic abilities at all, but he believed so hard that nobody could convince him otherwise.) He also had a piece of paper that he was convinced was the title deed to a nearby magical forest. He couldn’t read, but proudly showed everyone he met.

(The document actually urged people to scam him or trick him into servitude, since he was “a gullible, useless moron.”)