Excalibur is the sword of King Arthur in Sir Thomas Malory's iconic work Le Morte D'Arthur published in 1485 AD. The sword was originally introduced as Caliburnus (or Caliburn) in Geoffrey of Monmouth's History of the Kings of Britain (1136 AD) and developed by later authors before Malory immortalized it in his work. From its first appearance, the sword is a powerful weapon in the hands of a skilled warrior, and retains that reputation in every story it features.
(source; World History Encyclopedia, 2022)