Erfworld, The Thread.

[ChowGuy]

Yeah, but right before THAT he actually DOES become a king chess piece.

The progression into a chess piece starts before that, as he first loses his color, then becomes increasingly stylized with the radish on his crown assuming the traditional cross shape. Losing that is only the final stage. From the very beginning the symbolism is that he's becoming merely a piece in Charlies game rather then his own.