During his life, he made a replacement for the table on which Joseph of Arimathea placed the Holy Grail.  
In one story, he was originally named Ambrosius, and was brought to Vortigern as a sacrifice but is saved when he reveals two underground warring dragons.  He was later seduced by Nimue, who stole his magic and used it to imprison him.  According to Welsh legend, he made his way to an underground invisible glass house on Bardsey Island where he guards the Thirteen Treasures of Britain. During his life, he made a replacement for the table on which Joseph of Arimathea placed the Holy Grail.  FTP, name this legendary sorcerer, associated with King Arthur and the Knights of the Round Table.
In one story, he was originally named Ambrosius, and was brought to Vortigern as a sacrifice but is saved when he reveals two underground warring dragons.  
Merlin