Historically called the
The King - Slider - Value 1 or ∞ (depending on whether he is fighting or about to die) - can move one square in any direction, except when castling.
The battle is lost if the King is threatened with check or in check and cannot move out of check or cannot block the checking piece or cannot capture the checking piece.
The king cannot move into a checked position.
“A horse, a horse. My kingdom for a horse.”
Richard III's last words at the Battle of Bosworth Field in 1485