Flanderization
Flanderization is the process through which a fictional character's essential traits are oversimplified and exaggerated over a serial work.
The term Flanderization was coined by TV Tropes in reference to Ned Flanders of The Simpsons, who was increasingly caricatured over the show's run from a friendly and good-hearted Christian neighbor, among other characteristics, into a dogmatic, evangelical "Bible-thumper".
Flanderization is often associated with and cited as a consequence of "jumping the shark", a term used to demonstrate a creative work's gradual decline in quality which leads to a sudden decline in popularity.