Excalibur was a sword forged in a dragon's breath for Uther Pendragon to use against Vortigern. When Uther started to abuse the sword's power, Merlin took it from him and plunged it into a stone in a mountain cave and gave Uther an identical sword. Finally the sword was taken by Arthur from the stone and used as his sword. It was used to kill Mordred, and thrown back to Nimue in the Lake of Avalon.
After being burnished by The Red Dragon, it is described as a four foot, single-hand sword, with a round, studded pommel and ridged handguards. Its blade has golden runes engraved on it. When used in battle its blade sets itself ablaze.