Morgan le Fay
Morgan le Fay, along with Morgause and Elaine, was Arthur's half-sisters by his mother Igraine. She is often depicted as a witch and a villainess. Prior to Arthur's marriage, she tricked Arthur into sleeping with their sister, Morgause, who gave birth to Arthur's son and nephew, Mordred. Some legends say that Morgan le Fay was the mother of Mordred herself.
Morgan le Fay is sometimes known as Morgaine or Morgana.
She was involved in several plots against Arthur, including stealing the enchanted scabbard of Excalibur, trying to poison him with a magical robe, and killing some of his knights and subjects.
In many stories she is unhappily forced to marry King Urien, whom she also plots to kill.
Read more here and here
Morgan le Fay is sometimes known as Morgaine or Morgana.
She was involved in several plots against Arthur, including stealing the enchanted scabbard of Excalibur, trying to poison him with a magical robe, and killing some of his knights and subjects.
In many stories she is unhappily forced to marry King Urien, whom she also plots to kill.
Read more here and here
Mordred
Mordred was known to be Arthur's greatest enemy, sent to destroy him. His parents are Arthur's half-sister Morgause and Arthur himself. His step-father is King Lot of Orkney, and his half-brothers are the knights Gawain, Agravine, Gaheris, and Gareth.
With his ability to prophesize the future, Merlin warned Arthur that a boy born on May Day would grow up and cause the fall of both Arthur and the Knights of the Round Table. Hearing this, Arthur decreed that all boys born on May Day were to be placed on a ship and sent to Europe to find new families. Unfortunately, the ship was caught in a horrific storm and wrecked the ship before it reached its destination. Only one boy survived: Mordred. He was raised away from court until he was a teenager, and then he came to Camelot and joined the Round Table. His actual identity was unknown until it was too late.
Mordred was instrumental in uncovering the adultery of Guinevere and Lancelot to King Arthur, forcing him to sentence the queen to death. While Arthur pursued Lancelot, or in some stories the Roman Emperor Lucius, Mordred seized the throne and married Guinevere himself, forcing Arthur to abandon his battles in France and rush back to Britain. The two faced each other for the final time in the Battle of Camlann, which resulted in Mordred's death by spear at the hands of Arthur, but not before he mortally wounded his father/uncle and king.
In early versions of the legend, Guinevere has an affair with Mordred, not Lancelot.
More information on Mordred here.
With his ability to prophesize the future, Merlin warned Arthur that a boy born on May Day would grow up and cause the fall of both Arthur and the Knights of the Round Table. Hearing this, Arthur decreed that all boys born on May Day were to be placed on a ship and sent to Europe to find new families. Unfortunately, the ship was caught in a horrific storm and wrecked the ship before it reached its destination. Only one boy survived: Mordred. He was raised away from court until he was a teenager, and then he came to Camelot and joined the Round Table. His actual identity was unknown until it was too late.
Mordred was instrumental in uncovering the adultery of Guinevere and Lancelot to King Arthur, forcing him to sentence the queen to death. While Arthur pursued Lancelot, or in some stories the Roman Emperor Lucius, Mordred seized the throne and married Guinevere himself, forcing Arthur to abandon his battles in France and rush back to Britain. The two faced each other for the final time in the Battle of Camlann, which resulted in Mordred's death by spear at the hands of Arthur, but not before he mortally wounded his father/uncle and king.
In early versions of the legend, Guinevere has an affair with Mordred, not Lancelot.
More information on Mordred here.
Saxons? Lancelot?
Throughout the legend, Arthur and his knights fight various battles against outside sources. Those are most likely Saxon invaders, or remnants of the Roman army, or Irish invaders from the north, etc. Because each author is reflecting the values of his time on the legend, Arthur's enemies remain in shadow so that they can represent any enemy.
Later in the story, Lancelot becomes Arthur's enemy when it becomes known that he and Guinevere are having an affair. However, Arthur's pride is more wounded than any physical injury he sustained in any of the other battles he fought.
Later in the story, Lancelot becomes Arthur's enemy when it becomes known that he and Guinevere are having an affair. However, Arthur's pride is more wounded than any physical injury he sustained in any of the other battles he fought.