King (chess)

Castling

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White has castled kingside (0-0); Black has castled queenside (0-0-0).

Once per game, the king may castle in conjunction with a rook of the same color. When castling, the king moves two squares horizontally toward one of its rooks, and that rook is placed on the square over which the king crossed.

Castling is permissible under the following conditions:

• Neither the king nor the castling rook have previously moved.
• No squares between the two pieces are occupied.
• The king is not in check.
• None of the squares the king would move across or to are under enemy attack.

Castling with the h-file rook is known as castling kingside or short castling (denoted 0-0 in algebraic notation), while castling with the a-file rook is known as castling queenside or long castling (denoted 0-0-0).

Check and checkmate

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Black's king cannot move to squares under attack by the white bishop, knight, queen, or pawn. Since White is checking Black, and Black can neither move, capture the checking piece, nor block the check, Black is checkmated.

A king that is in a square controlled by an enemy piece is said to be in check, and the player in check must immediately respond the situation. There are three possible ways to remove the king from check:

1. Capturing the checking piece. This is done with either the king or another piece, but the king cannot be placed in check from a different piece in the process.^[3]
2. Moving the king. The king is moved to an adjacent square where it is not in check. The king is not allowed to castle when it is in check.^[3]
3. Blocking the check. Also called interposing, this is possible only if the checking piece is a queen, rook, or bishop and there is at least one empty square in the line between the checking piece and the checked king. Blocking a check is done by moving a piece to one such empty square. (The blocking piece is then pinned to the king by the attacking piece.)^[3]

If none of the three options are available, the player's king has been checkmated, and the player loses the game.^[3]

If the king is under attack by two different pieces simultaneously (referred to as double check), it is not possible to capture or block both of them simultaneously so the king must move.^[4]

In casual games, when placing the opponent's king in check, it is common to announce this by saying "check", but this is not required by the rules of chess. In tournament games, it is unusual to announce check; competent players are expected to know when they are in check.^[5]

Stalemate

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	a	b	c	d	e	f	g	h

White to move: White cannot move legally because of the black queen and king. Since the king may not move into check, White is stalemated.

A stalemate occurs when a player, on their turn, has no legal moves, and the player's king is not in check.

If this happens, the king is said to have been stalemated, and the game ends in a draw. A player who has very little or no chance of winning will often, in order to avoid a loss, try to entice the opponent to inadvertently place the player's king in stalemate (see swindle).^[3]

c. 600 CE Raja (India) Chaturanga

The earliest documented chess king was known as the Raja. This piece could move one square in any direction and determined the outcome of the game, a feature that remains in modern chess.^[9]

c. 7th-9th centuries Shah (Persia and the Islamic world) Shatranj

In Shatranj, the king was called the shah, a name that helps derive the terms “check” and “checkmate.” (Checkmate, 2024) According to Shatranj rules, if only the king remained on the board, it was a loss unless the opponent was in the same position, which resulted in a draw. Additionally, a stalemate was counted as a win for the player delivering the stalemate.^[10]

c. Late 15th century, early modern chess

Castling was introduced in medieval Europe, where different regions had their own rules. One example was the “king’s leap,” which let the king move two squares. Early versions of castling took two moves: first, the king moved two spaces, then the rook moved next to the king.^[11]

Modern chess

By this time, the rules for the king, including castling, check, and checkmate, had been standardized across Europe. Stalemate was officially defined as a draw.^[9]

Shouldering

Another common endgame technique is shouldering. In this strategy, a king deliberately occupies a path that prevents the opposing king from approaching critical areas of the board, often pushing the rival king further away from the action. Shouldering is frequently decisive in races to support passed pawns.^[13]

Centralisation

In the endgame, the king’s value as a fighting piece increases dramatically. Because there are fewer threats of checkmate, the king can safely advance toward the center of the board. A centralized king controls a wide range of squares, assists in pawn promotion, and exerts influence over both flanks.^[14]

Opposition

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Opposition

One of the most fundamental strategic ideas in king endgames is the opposition. Opposition occurs when two kings stand on the same file, rank, or diagonal with only one square separating them. The player not having the move is said to “have the opposition.” This forces the opposing king to yield ground, and is often the critical factor in achieving promotion of a pawn or preventing the opponent’s advance.^[15]

Outflanking

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Outflanking

Closely related to opposition is the concept of outflanking. When direct opposition cannot be maintained, a king can maneuver around the opponent’s king to gain access to key squares. Outflanking allows a player to break through an opponent’s defensive setup, especially in pawn endgames, and is often combined with zugzwang to force progress.^[15]