Tyrek was the bastard son of a woman in the employ of Casterly Rock.
Tyrek served as a cup bearer at Casterly Rock until Damon Lannister found him work as a stable boy.
After the murder of his mother, Tyrek fled Casterly Rock on a stolen horse and made his way north. On his way through the Oldstones, three members of the Burning Hand's Men waylaid him and stole his horse. Having nowhere else to go and no other options, Tyrek opted to join them rather than turn south and face the punishment of the law.
Near the end of the third era, Tyrek witnessed the death and capture of nearly all the men at Oldstones by a group of Lannister soldiers led by Arthur Swyft. His mentor and friend Tanglefoot Ben helped him hide, and was then killed in front of his eyes.
The eighth era found Tyrek north of Last Hearth, holed up on a small farmstead during the worst winter in recent memory. Ill-prepared for the severity of the coming season, the old man who'd lived there with him had died and Tyrek buried him, deciding to travel north afterwards in the hopes of finding food and shelter elsewhere, but only coming upon a farmstead and its three dead occupants instead.
Tyrek arrived at the Wall shortly thereafter, joining a group of new recruits and being given the nickname "the Maiden" by the Master-at-Arms, Ser Ormund Dondarrion. He is chosen out of the pool of new recruits to help beat another boy bloody as a lesson.
"The men had taken to calling him Sand, after the colour of his hair. When they had left the stream behind the large man had grunted that he “looked the bastard sort” and the name had stuck." - Blood and Whispers
"...a pretty-looking man with a shock of muddy blonde hair..." - Arstan Selmy
"The Maid was stood beside (Arstan) now with that same look on his face as before, some exhaustion of the soul which showed only in his eyes." - Arstan Selmy