Who is Morgan Le Fay?

According to the Arthurian legends, Morgan Le Fay is
Arthur's half-sister.  She is a priestess, and has spent much of her time at Avalon with
the other mystical women of the time period.  When Arthur came of age, he was expected
to celebrate this rite of passage by mating with a priestess from Avalon.  Unbeknownst
to Arthur and Morgan Le Fay, the pairing for this rite, they are related.  As a result
of this pairing, the two produce Mordred, Arthur's illegitimate son, who is responsible
eventually, for Arthur's death.  The two are at odds with one another as Mordred is
jealous and upset that he is not recognized as the King's son and treated with more pomp
and circumstance.

Morgan Le Fay, a dark beauty, is angry
with Arthur, too, because he prefers the fair beauty of Gwenivere to herself.  So, in a
way, both she and Mordred have been snubbed by Arthur.  This is probably why she would
have tested Arthur and his knights of the Round Table in terms of their honor, bravery,
generosity, and willingness to protect those who are weak and unable to protect
themselves (women, children, elderly, etc.).