The Lady of the Lake is thought to have been based on lake fairies in Welsh stories.
Geoffrey of Monmouth cites the leader of the maidens of Avalon as Morgan Le Fay. However later stories say that the Lady was their ruler. It seems probable that the two were aspects of the same character. Indeed, both appear among the three queens who escort Arthur to Avalon, and they may well represent the Celtic Triple-Goddess.
Many legends say the Lady of the Lake was responsible for educating Lancelot. She is known by many names, including Vivien and Nimue. She is also said to be the one who locked Merlin away with his own spell.
The Lady is the person who gave Arthur Excalibur and then took it back when Bedivere threw it back into the lake. She is also said to have intervened when Morgan Le Fay gave Excalibur to Accolon, who tried to kill the king with it.
Merlin fallen deeply in love with her and he taught her all his magical powers. Over the years Merlin taught her so well that the Lady of the Lake became a better magician even than Merlin. She imprisoned him in Glass Tower. The lack of Merlin's help contributed to Arthur's downfall. The Lady of the Lake was unable to fulfil Merlin's role as magician to Arthur,