The king (♔, ♚) is the most important piece in the game of chess. It may move to any adjacent square that is not controlled by an enemy piece; it may also perform, in tandem with the rook, a move called <em>castling</em>. If a player's king is threatened with , it is said to be <em>in check</em>, and the player must remove or evade the threat of capture immediately, such as by moving it away from the attacked square. If this cannot be done, the king is said to be in <em>checkmate</em>, resulting in a loss for the checkmated player. A player cannot make any move that places their own king in check. Despite this, the king can become a strong offensive piece in the endgame or, rarely, the middlegame.

In algebraic notation, the king is abbreviated by the letter K among English speakers. The white king starts the game on e1; the black king starts on e8. Unlike all other pieces, each player can have only one king, and the king is never removed from the board during the game.

A king can move one square horizontally, vertically, and diagonally unless the square is already occupied by a friendly piece or the move would place the king in check. If the square is occupied by an undefended enemy piece, the king may capture it, removing it from play. Opposing kings may never occupy adjacent squares (see opposition) to give check, as that would put the moving king in check as well. The king can give discovered check, however, by unblocking a bishop, rook, or queen.

Castling

Once per game, the king may <em>castle</em> 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).

Status in games

Check and checkmate

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 to the situation. There are three possible ways to remove the king from check:

  1. . 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.

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.

Stalemate

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).

It is not meaningful to assign a value to the king relative to the other pieces, as it cannot be captured or exchanged and must be protected at all costs. In this sense, its value could be considered infinite. As an assessment of the king's capability as an offensive piece in the endgame, it is often considered to be slightly stronger than a bishop or knight. Emanuel Lasker gave it the value of a knight plus a pawn (i.e. four points on the scale of chess piece relative value), though some other theorists evaluate it closer to three points. It is better at defending friendly pawns than the knight is, and it is better at attacking enemy pawns than the bishop is.

History

thumb|The Indian chess king represented here by the Maharaja seated upon a tall elephant in a Howdah

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.

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.

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.

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.

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.

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.

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.

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. the king typically measures about 3.75 inches (95 mm)