Flanderization/Professional Wrestling

The Undertaker went from being simply, well, an undertaker to becoming almost literally a god of death and the occult. Briefly reversed when he became a "biker" character for a few years.
- Paul Bearer was no stranger to this trope either, with his voice and mannerisms getting progressively goofier over the years. Compare this early 1991 promo to this later 1994 promo.
Stone Cold Steve Austin, anyone? At the height of his popularity, he was simply a very tough working-class guy who was lashing out at the oppression of the modern world. Over time, the "underdog" side of his character became deemphasized and the "rebel" side became predominant, with the inevitable result that he devolved into an unabashed Jerkass - and the fans still cheered him!
Inverted with Triple H, who started out as an Upper Class Twit but eventually developed into a fairly normal, non-pretentious guy who just happens to be very rich.
Towards the end of his wrestling career The Rock's character had pretty much just degenerated into nothing but his most popular catchphrases, gestures, and moves. Probably why Dwayne Johnson decided to stick with the move to Hollywood acting even after some of his early attempts weren't that successful.