Alyn was born the son of a sheep farmer and was raised in a small shack perched on the side of the Dragonmont. As boy he was injured in a rock-slide and (the then Crown Prince) Aerys Targaryen order that Dragonstone’s maester heal the unfortunate lad. Once mended Alyn chose to stay at the castle, serving first as a page, then squire, and then knight of House Targaryen. Alyn was instrumental in training Prince Rhaegar in the martial arts. During the waning days of the Targaryen dynasty Alyn was named castellan of Dragonstone by Queen Rhaella.

During the Assault on Dragonstone Alyn commanded the garrison to fight to the last man; for every moment that Stannis was unaware that the prince and princess had fled was one more moment they had to reach safety. Alyn positioned himself in the royal apartments, and when Ser Darron entered the room Alyn made it clear he had made his peace with dying in Dragonstone. It was then that Alyn charged Darron, dealing a vicious blow. Darron, maneuvered Alyn to the side, opening a line of sight for Jardon. With Darron’s Valyrian steel and Jardon’s crossbow Ser Alyn’s life was taken from him.