Chedoku is an extremely complex board-game. The name is a portmanteau of Chess and Sudoku, and the rules combine elements of both. Chedoku is a strategy game for two players, played on a nine-level board, though a simplified, three-level variant attained wide popularity during the last century of the Planetary League. The pieces are based on chess pieces, but in addition to moving and capturing opposing pieces, they also place or modify numbers associated with each square. These numbers in turn constrain the movement of the pieces.

The game tends to be complex enough as to be essentially unintelligible to most humanoid life. The main competitors and audience for Chedoku lies among beings adapted for high intelligence. Encephaloids, Brains, and powerful AIs are the main competitors. Occasionally, a highly intelligent human or other humanoid will make an appearance in an official tournament, but rarely lasts beyond the opening matches.