ChessKing

The ChessKing can move to any orthogonally or diagonally adjacent square, thus giving it about as much attacking power as a minor piece. It is not usually used in an attacking role, however, as it is Royal; i.e. its loss is the end of the game. (in WesternChess and most variants, the ChessKing is never actually captured; merely its inability to escape from check ends the game. This is known as CheckMate).

In WesternChess endgames, the board is usually empty enough for the ChessKing to emerge without fear of being CheckMated, and so he usually does, realizing his full worth as an attacking piece. In a lot of chess variants, the endgame in similar in nature, and the ChessKing becomes similarly useful. In BugHouse and ChesSers, however, since the boards do not, as a rule, clear up over time, the ChessKing spends the entire game in a small fortress, until he is evicted and CheckMated.

In NuclearChess?, the ChessKing is the only piece that can survive capturing something (if you're playing RadiationSuit rules).