Arthur Dayne

"Ser Arthur Dayne, the Sword of the Morning... led the attack on the Kingswood Brotherhood. Defeated the Smiling Knight in single combat."

- King Joffrey Baratheon

Arthur Dayne is an unseen character in Game of Thrones. He is not expected to appear in the series, being long dead by the time it starts. Ser Arthur Dayne was a knight of House Dayne who bore the title of "the Sword of the Morning" and a member of the Kingsguard of Aerys II Targaryen.

Background
Ser Arthur was the second son of Beric Dayne, Lord of Starfall. As the wielder of the sword Dawn, which had been forged from the metal of a fallen star, he bore the title of "the Sword of the Morning".

Season 4
While checking The Book of Brothers, King Joffrey Baratheon passingly reads through the entry on Ser Arthur Dayne, mentioning his leading of the attack on the Kingswood Brotherhood and his defeat of the Smiling Knight, one of its members, in single combat. The Book of Brothers also mentions he was granted temporary command over the Kingsguard after Lord Commander Gerold Hightower suffered injuries. He perished in Robert's Rebellion alongside Ser Gerold and Ser Oswell Whent at the Red Mountains of Dorne, fighting Lord Eddard Stark.

In the books
In the A Song of Ice and Fire novels, Ser Arthur Dayne was a knight who had achieved legendary status by the time the events of the books take place. As the wielder of the greatsword Dawn, a blade said to have been forged from metal from the heart of a fallen star, he bears the title of "the Sword of the Morning". He was a close friend of Prince Rhaegar Targaryen.

It was Arthur Dayne who knighted Jaime Lannister as a reward for his valor at the battle against the Kingswood Brotherhood.

Arthur Dayne is remembered as the greatest knight of his generation, not only in martial skill but in value and virtue as a true knight. Even Barristan Selmy, a living legend in his own right, thought that Ser Arthur surpassed himself in all respects. Ser Barristan, Jaime Lannister, and even Eddard Stark were all in awe of Ser Arthur, and recall him with nothing less than complete reverence. The fact that Arthur Dayne used to stand by and do nothing while the Mad King performed his atrocities did not taint his reputation at all.

When asked who would win in a duel, George R.R. Martin said that if Arthur Dayne and Barristan Selmy fought with any swords it would be a very even fight - but if Dayne was armed with his sword Dawn, he would narrowly have the advantage over Selmy.