"I've got Morgana again and I've got about six of her... do you want it? You can start collecting."
-- Ron Weasley to Harry on the Hogwarts Express (PS6)
Morgana, also known as Morgan le Fay, was a powerful Dark witch in the Middle Ages, Queen of the Island of Avalon, and half-sister to King Arthur. She was Merlin‘s greatest enemy (FW).
Morgana was an Animagus, taking the form of a bird. She was skilled at healing magic (FW).
Other canon notes and references
Ron owned six of her Chocolate Frog Cards so he gave one to Harry during their first trip to Hogwarts (PS6).
The famous witch Morgana, like Merlyn, figures into the King Arthur legend. According to the legend, Morgan le Fay, or Morgana, was the witch in the castle that Wart and Kay encountered with Robin Wood (Robin Hood for the unenlightened), Maid Marian, Little John, and the merry men to rescue Friar Tuck, the Dog Boy, and an old man named Wat. Morgana was the child of the Duke of Cornwall and Igraine, the woman Uther Pendragon seduced to have Arthur. (contributed by William Givens)
Though according to legend King Arthur's reign was sometime around the 6th/7th centuries, in Rowling's world Morgana must have lived around 1000 (at the earliest) as her contemporary, Merlin, attended Hogwarts, which wasn't founded until around 990.