An active king is a king used as a fighting piece in the endgame, marching toward the centre or enemy pawns instead of hiding behind cover.
In the opening and middlegame the king is a liability to be tucked away. Once most pieces are traded and the danger of mate fades, the king becomes a strong attacker — roughly as valuable as a minor piece for fighting purposes.
An active king supports your passed pawns, blockades or wins the opponent’s pawns, and out-muscles a passive enemy king for key squares. In many endgames the side whose king reaches the centre first simply wins.
The practical rule: when the queens come off, bring your king toward the action without delay. Centralization is often worth a whole tempo and frequently the difference between a win and a draw.
Once the queens and most pieces are gone, so the risk of a sudden mating attack is low. From that point the king should head toward the centre and the enemy pawns as fast as possible.
For attacking and defending pawns it’s worth roughly a minor piece. In king and pawn endgames it’s the strongest unit on the board, and the side that centralizes first often wins outright.
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