The sword of Charlemagne in the Matter of France, the name of which means »Jubilant«. It was forged by Galas, of the same steel as Flamberge (one of many swords to bear that name) and Hauteclaire; some claim instead that it was originally the sword of Galahad. It changed color thirty times a day; its pommel contained the head of the Lance of Longinus, and its blade was supposedly peerless, although Quatrelle claims that it was destroyed along with the other swords of Ansias, Galas and Munifican by Oliver, who struck them a blow with his own sword Glorieuse.
As is the case for many other important historical objects, there are several swords claimed to be Joyeuse, all of which are fake. One of these is held in the Louvre, and is worth some attention: despite not being genuine, it is a sword of some antiquity (possibly as old as the 10th century) and was owned by the Valois kings of France, and used as a proof of their right to the throne. Several portraits of French kings depict them wearing this sword, notably Hyacinthe Rigaud's portrait of Louis XIV, the Sun King, perhaps the most famous of all pictures of kings. It may have occurred to you to wonder why the king, in this portrait, is manifesting such an incredibly ridiculous pose. Look at the picture again: what is in the center of it, what is he turning himself to reveal, what is he lifting his capes to expose?
Such symbolism was no doubt seen as important by a man who had proclaimed himself absolute monarch — or perhaps it's something simpler and more pugnacious, a message to his enemies: μολὼν λαβέ, fuckers.