What are your favorite negative character arcs?

A negative character arc is one where the protagonist gets worse over time rather than better. They might or might not turn for the better in the end, but the majority of the time is spent on a negative descent.

A well-done example would be Frodo. The ring wears him down through the course of the story.

An example that should have been good but wasn’t executed as well as it should have been, would be Anakin in the Star Wars prequel.