King (chess)

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 castling. If a player's king is threatened with capture, it is said to be in check, 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 checkmate, 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.

The white king starts on e1, on the file immediately to the right of White's queen from White's perspective. The black king starts on e8, directly across from the white king and left of the queen from Black's perspective. Each king starts on a square opposite its own color.

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.

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:

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 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: