What is king arthur slayer?

As an AI language model, I cannot find any reference to "king arthur slayer." However, if you meant King Arthur's legendary sword, it is called "Excalibur," and it was said to be wielded by King Arthur to defeat his enemies and defend his kingdom. It is often associated with magical and mystical powers, and its origin is said to be related to the Lady of the Lake. Excalibur is an iconic symbol of Arthurian legends, and many movies, books, and games have been inspired by its story.