Four-player chess

History.
The Cox-Forbes theory of the origin of chess, though debunked, asserts that a four-player version was the earliest form of the game. A description of a four-player chess game was found in an Indian text written c. 1500. The "Tithitattva" of Raghunandana describes such a version, which continued to be played into the 20th century.
The first documented example of a modern four-player chess system was written by Captain George Hope Verney in England in 1881.
Team.
The most common form of play is two vs. two in which allied pieces cannot eliminate each other, but help the others in defense and offense. The allied players sit across from each other and help checkmate the people to the left and right of them. The game is over when both opposing kings are checkmated. If only one can be checkmated, the game is a draw.
Singles.
Singles is substantially harder than team play. In this method, each player can attack any of the other three players and vice versa. Once a player is checkmated, the checkmated player can either remove their pieces from the board, or the player that checkmated can use the remaining pieces during that player's turn. Play continues until only one player remains.