Chair of Experimental Serendipity
Rincewind. "Serendipity" means "the effect by which one accidentally stumbles upon something fortunate, especially while looking for something entirely unrelated". That practically defines Rincewind, as he seems to end up saving the world while trying to, say, find a potato, or run away. All Ridcully has done is made it his official job, along with eighteen or so other titles, chairs, and posts.