The Winged Knight was a legendary First Man figure of the Vale from the Age of Heroes thousands of years before the coming of the Andals. He is sometimes conflated with Ser Artys Arryn, an Andal who conquered the Vale for House Arryn and was known as the "Falcon Knight".
Among the hundreds of stories told about him, the Winged Knight is said to have flown upon a huge falcon and had armies of eagles at this command. He won the Vale by slaying the Griffin King atop the Giant's Lance. He is said to have been friendly with giants and merlings. His wife, one of the children of the forest, died giving birth to his son.
The existence of the Winged Knight is questioned by Maester Yandel, who includes the knight with other legendary heroes such as Lann the Clever and Bran the Builder. Archmaester Perestan theorized that the story of a huge falcon derives from dragonriders.
Yandel suggests that singers combined the figure of the Winged Knight with that of Ser Artys Arryn, who won the Vale for the Andals from the First Men in the Battle of the Seven Stars, to curry favor with the Kings of Mountain and Vale from House Arryn. The Arryn legends state the Winged Knight drove the First Men from the Vale.
A Feast for Crows
Young Lord Robert Arryn's favorite stories are those of the Winged Knight. He demands three stories of Ser Artys Arryn from Alayne Stone before he agrees to prepare for his departure from the Eyrie. Alayne agrees she will only tell the stories after they reach the Gates of the Moon.
The Winds of Winter
This information has thus far been released in a sample chapter for The Winds of Winter, and might therefore not be in finalized form. Keep in mind that the content as described below is still subject to change.
After Alayne notices that Robert is always comforted when she reads him tales of his legendary ancestor, Ser Artys Arryn, the Winged Knight, she has the idea that he would feel safer if he were surrounded by his own bodyguard of Winged Knights. Lord Petyr Baelish, regent for Robert, likes her idea and immediately set plans in motion to form the Brotherhood of Winged Knights. The winners of a tourney at the Gates of the Moon will become the first eight members of the new knightly order, and serve Robert for the next three years. Sixty-four knights from across the Vale of Arryn come to the tourney to compete for the eight positions.
The Winged Knight was brave, and so am I.
Alayne: You're my winged knight, Ser Sweetrobin.
Robert: The Winged Knight could fly.Alayne: Higher than the mountains.