Chess is especially popular for its complexity. The number of legal positions in chess is estimated to be 1043; the number of possible games is a lot larger and greatly exceeds the estimated number of particles in the observable universe.
Chess originated from the Indian game Shatranj, about 1400 years ago. This game moved east and became xiang4 qi2 (象棋 Chinese Chess) in China, and Shogi in Japan. It migrated west, reached Europe in the 10th century, and evolved through various versions such as Courier. By the 15th century, the game in Europe was almost the same as is played today. The current rules were finalized in the early 19th century.
Each player is given sixteen pieces which are arranged in the opening position on a 64-square chess board. The players alternate moves (one has the White pieces and moves first, the other has the Black pieces). The object of the game is checkmate, a situation where the opponent's king is threatened with capture and has no way out. A position in which the king is threatened with capture (but has a way out) is called check; a player can never move a king into and must always rescue a king from such a position.
If a player is not in check and has no legal move, then the situation is called stalemate and the game ends as a draw. Draws may also be claimed if the same board position repeats itself exactly for the third time, or if fifty moves are played without a piece being taken or a pawn moved.
The most powerful piece is the queen. The queen can move in a straight line in any direction unless blocked by another piece. In contrast, rooks can move in a straight line only in non-diagonal directions, and bishops can move in a straight line only in diagonal directions.
The knight moves by 'jumping' in an L-shaped pattern, two squares in any non-diagonal direction and then one square perpendicular. The knight is the only piece that may jump over other pieces to reach its destination.
Pawns move straight forward by one square (or two from their starting position). They capture diagonally forward. If a pawn reaches the 8th rank, it can be promoted to any other piece except a king.
In tournament play and for quick chess, a chess clock is used; each player presses a button after every move and the clock keeps track of the time used. In correspondence chess, the moves are sent by mail and every player is given a set number of days per move.
Some rules of thumb for playing well are given on the Chese Strategy and Tactics page.
Lists of World Champions and famous players are available.
In May 1997, a computer (IBM's updated [Deep Blue]?) defeated the then reigning world champion Gary Kasparov in a match. IBM keeps a web site of the event at http://www.chess.ibm.com. While not an official world championship, the outcome of the match is often taken to mean that the strongest player in the world is a computer. IBM retired Deep Blue after the match and it has not played since.
The world organization of chess players is the FIDE which organizes regular world chess championships. Recently, some players complained about arbitrary decisions by FIDE and left to start competing organizations.
There are several variants of chess: suicide, where capturing moves are mandatory and the object is to lose all pieces, Fischer Random where the placement of the pieces on the 1st and 8th rank is randomized to disemphasize the value of opening theory, tandem where two teams of two players face each other on two boards and the pieces captured by one partner can be placed on the board by the other, and advanced chess where the players are allowed to consult a computer.
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