king (chess)
The king (♔, ♚) is the most important piece in the game of chess. The king can move one square in any direction (orthogonally or diagonally), and also has a special move known as "castling". If a player's king is threatened with capture, it is said to be in check, and the player must remove the threat of capture on the next move. If this cannot be done, the king is said to be in checkmate, resulting in a loss for that player. Players 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 in the middlegame.
Each player begins the game with a king of their color. In algebraic notation, the king is abbreviated in English by the letter K. The white king starts the game on e1; the black king starts on e8. Unlike the other pieces, only one king per player can be on the board at any time, and the kings are never removed from the board during the game.
White starts with the king on e1, on the first rank to the right of the queen. Black starts with the king on e8, directly across from the white king. The kings always start on a square of opposite color.
A king can move one square in any direction (horizontally, vertically, or diagonally), unless the square is already occupied by a friendly piece, or the move would place the king in check. As a result, opposing kings may never occupy adjacent squares (see opposition) to give check, as that would put the moving king in check as well. However, the king can give discovered check by unblocking a bishop, rook, or queen. The king is also involved in the special move of castling
The king can make a special move, in conjunction with a rook, called castling. When castling, the king moves two squares toward one of its rooks, and that rook is placed on the square over which the king crossed. Castling is permissible only when:
neither the king nor the castling rook have previously moved
no squares between them 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).
A king that is under attack is said to be in check, and the player in check must immediately remedy the situation. When placing the opponent's king in check, it is common to announce "check", but it is not required by the rules of chess. There are three possible ways to remove the king from check:
The king is moved to an adjacent non-threatened square. A king cannot castle to get out of check. A king can capture an adjacent enemy piece if that piece is not protected by another enemy piece.
A piece is interposed between the king and the attacking piece to break the line of threat (not possible when the attacking piece is a knight or pawn, or when in double check).
The attacking piece is captured (not possible when in double check, unless the king captures).
If none of the three options are available, the player's king has been checkmated and the player loses the game.
In the opening and middlegame, the king will rarely play an active role in the development of an offensive or defensive position. Instead, a player will normally try to castle and seek safety on the edge of the board behind friendly pawns. In the endgame, however, the king emerges to play an active role as an offensive piece as well as assisting in the promotion of their remaining pawns.
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) (Lasker 1934:73). It is better at defending nearby pawns than the knight is, and it is better at attacking them than the bishop is (Ward 1996:13)