I think all four of them changed a lot over the course of the show. They went from reasonable people with their own quirks to completely unlikeable jerks by the last season.

I never thought they were unlikeable I guess. They could sort of be jerks at times but a lot of times you could also kind of see where they were coming from. I always kind of thought they were self centered people, shallow people with quirks and pretty much only accepted people within their group of friends for the most part.

Every character in The Office seemed to change by the time the finale aired. Some were more subtle(Dwight and Jim) then Andy was all over the place. He changed each episode.

The youngest Taylor boy on Home Improvement went from being your typical baby faced younger sibling to dressing like a goth as a teenager.

Al Lambert on Step by Step started the show as a tomboy as a child. By the end of the show she was more into wearing dresses and feminine clothes.

This will go over most peoples heads, but Screech and Mr. Belding changed by the end of Saved by the Bell: The New Class. In the original they Screech was socially awkward and Belding was the wise mentor to his students. By the end of TNC, Screech was a walking cartoon, and Belding was nothing but an excuse for slapstick.

Any that were sponge-worthy of course.

Supposedly, Ted Knight on The Mary Tyler Moore Show didn't like the way his character was being portrayed. So the writers changed him (a bit). I wish I had the exact quote, but a TV critic claimed that Ted Baxter went from being a one-dimensional idiot to a multi-dimensional idiot.

He often did in his pants.

Exactly just came in to post that.

He was cool then he completely jumped the shark.