Did you see the pilot that was made with Jack Carter as Arthur?
Originally Jerry Stiller turned down the role of Arthur and the part went to actor Jack Carter instead. After a pilot was shot Stiller changed his mind and Carter got the boot. They then reshot Arthur's scenes with Stiller.
Here is a clip of Jack Cater as Arthur
https://www.youtube.com/watch?v=7DG0mFuZJTI
It gives such a different vibe to the show imo and, even though he isn't the main character, I wonder how successful the show would have been without Stiller.