An empress is a fairy chess piece piece that can move like a rook or a knight. It cannot jump over other pieces when moving as a rook, but may do so when moving as a knight. The name empress has been suggested by some scholars as the preferred name for this piece, but is much more widely known as chancellor or marshall (or marshal). It may also be simply called the rook+knight compound. Chess diagrams in this article use RN as notation for the empress.
The empress is one of the most simply described fairy chess pieces and as such has a long history and has gone by many names. A generic name would be the rook+knight compound. The name chancellor was introduced by Ben Foster in his large variant Chancellor Chess (chess on a 9×9 board, with a chancellor on the opposite side of the king as the queen), and the name marshal was introduced by L. Tressan in his large variant The Sultan's Game. José Raúl Capablanca used both in his large variant Capablanca chess: he originally called this piece the marshal, but later changed it to chancellor. Coincidentally, chancellor was his original name for the archbishop. Both chancellor and marshal are popular names for the rook+knight compound, although a case could be made for marshal, as the word is related to mare (female horse) and thus fits better for a piece that can move like a knight than chancellor, which has no connection to horses. Also, there are many commonly used chess pieces that, like chancellor, begin with C (e.g. the cannon in xiangqi, the camel in Tamerlane Chess, the champion in Omega Chess, and the cardinal or princess), and using the name marshal for the rook+knight compound would reduce this difficulty.
The name empress is more widely used among problemists. By analogy with the queen, which is a rook+bishop compound, it was suggested that the three basic combinations of the three simple chess pieces (rook, knight, and bishop) should all be named after female royalty. Since the rook+knight compound seemed to be obviously stronger than the bishop+knight compound (as the rook is stronger than the bishop), the name empress was used for the rook+knight compound and the bishop+knight compound was called the princess. However, the bishop+knight compound can get (but not force) checkmate of a lone king by itself (with the king in a corner and the attacking archbishop two squares diagonally away), while the rook+knight compound cannot. Worse, the word empress suggests a piece stronger than the queen, while this piece is at best equal to and perhaps weaker than the queen, especially in the endgame.
The empress was first used in Turkish Great Chess, a large medieval variant of chess, where it was called the war machine (dabbabah; not to be confused with the piece more commonly referred to as the dabbaba today, which is the (2,0) leaper). It was introduced in the West with Carrera's chess from 1617, where it was called a champion, and has been used in many chess variants since then.
Ralph Betza (inventor of chess with different armies, in which the empress was used in one of the armies) rated the empress as about nine points, equivalent to a queen, as the knight and bishop were about equal and the empress and queen were simply the knight and bishop with the power of a rook added to both. He noted that the queen may be slightly stronger than the empress in the endgame, but that the empress, on the other hand, has a great ability to give perpetual check and save a draw in an otherwise lost game. Unlike the queen, which can move in 8 different directions, the empress can move in 12.
In the endgame of king and amazon (queen+knight compound) versus king and empress, the weaker side may force a draw by setting up a fortress. These fortresses force the side with the amazon to give perpetual check, as otherwise the side with the empress can force a simplification or give its own perpetual check. King and empress versus king is a forced win for the side with the empress; checkmate can be forced within 11 moves. In comparison, the queen requires 10 moves and the rook requires 16.
The drawing positions in the queen versus pawn endgame do not exist in the empress versus pawn endgame.
Many chess variants use a rook+knight compound, but due to its powerful ability, it is uncommon for variants to use more than one per colour on a normal 8×8 board. Seirawan Chess uses one such piece (called elephant) per colour. Musketeer Chess allows the players to introduce up to one chancellor each on an 8×8 board. Capablanca Chess uses one chancellor per colour on a 10×8 board. When the playing area is larger, the ratio of squares which powerful pieces can control is decreased, and variants will then often have a greater combination of powerful pieces. Waterloo Chess uses two marshalls of each colour on a 10×10 board, and Chess on an Infinite Plane uses two chancellors of each colour on an unbounded playing area.