The legendary sword used by heroes and kings. It has a great power that is unmatched by any other weapon. It turns out that anyone can use Excalibur. However, no one can put up with its personality (it has a bigger ego than Black Star). The only reason that those who use it are called heroes is that they can put up with its annoying habits, such as a list of one-thousand things he demands to be completed, such as daily five-hour reading sessions. Excalibur was first introduced when Kid and Black Star found a book about him and thus sought him out, only to discover that the book had in fact been written by Excalibur himself. They quickly ditched him due to his personality. His other form is completely the opposite given his elegant weapon form, looking like a cartoon-ish gentlemen with an outrageous mustache and no pants. On the other hand, his legendary powers have been proven by a fellow Shibusen student who found completing the appointed tasks easy. Excalibur can grant great power, light speed and teleportation, and the wielder can easily defeat three of Shibusen's strongest combined. In the end, Excalibur was put back again because the student could not put up with his annoying sneeze. His existence throughout the story is purely comical, with the exception of the fact of how he informed Kid, the Thompsons, Buttataki, and Blair about the story of Eibon, backed by Shinigami.

(From Wikipedia)