Appearance and Character
He is well renowned for his tracking ability within the Night's Watch.
A Game of Thrones
When Jon Snow and Samwell Tarly go to the haunted forest to swear their vows, Dywen is among the rangers who escort them. He is the first to notice the human hand that Ghost found. Dywen accompanies Lord Commander Jeor Mormont when he goes to look at the corpses of Othor and Jafer Flowers in the haunted forest.
A Clash of Kings
Dywen is among the great ranging, the two hundred brothers of the Night's Watch that leave Castle Black to search for the wildlings. While camped out on the Fist of the First Men, Dywen senses the smell of cold, to the disbelief of his brothers with the exception of Jon, who also understands the cold as a sign of wights and the Others.
A Storm of Swords
Dywen is one of those selected to die by Chett's conspirators on account of his excellent tracking abilities. Before the plot can begin, however, the Fist of the First Men is attacked by wights. Dywen is among the survivors of the attack.
Once at Craster's Keep, Dywen is one of the few men that takes Samwell Tarly seriously when he tells the men he slew an Other with his dragonglass dagger. Dywen joins Dolorous Edd in making Sam and Grenn tell the Lord Commander the tale. 
Dywen stays loyal to the Watch during the mutiny at Craster's Keep, in which Lord Commander Mormont is slain. He is one of the few survivors of the ranging to make it all the way back to Castle Black.
A Dance with Dragons
Dywen is one of the most outspoken rangers against the proposal to seal off the gates and other entrances of the Wall to prevent the Others and more wildlings from passing. He argues threats like Tormund Giantsbane and the Weeper would either cross the Bridge of Skulls or pass through an unseen gate, trapping the Night's Watch unnecessarily. He rallies most of the rangers under Jon, whereas the builders and stewards side with Bowen Marsh.
Lord Commander Jon Snow appoints Dywen as the leader of one of three groups of three rangers sent ranging. His group includes Ser Alliser Thorne. Melisandre warns Jon soon after their departure that in her visions she has seen three of the nine rangers return eyeless, weeping blood.
When the decapitated heads of the group led by Black Jack Bulwer turn up north of Castle Black, Owen the Oaf inquiries if Dywen was among the casualties. Jon asks Melisandre if she has also seen the surviving six rangers, including Dywen, in her visions. Melisandre reveals she has not seen their fates just yet.
—thoughts of Jon Snow
- A Storm of Swords, Prologue.
- A Clash of Kings, Chapter 34, Jon IV.
- A Game of Thrones, Chapter 48, Jon VI.
- A Game of Thrones, Chapter 52, Jon VII.
- A Clash of Kings, Chapter 6, Jon I.
- A Clash of Kings, Chapter 13, Jon II.
- A Storm of Swords, Chapter 33, Samwell II.
- A Storm of Swords, Chapter 48, Jon VI.
- A Dance with Dragons, Chapter 7, Jon II.
- A Dance with Dragons, Chapter 17, Jon IV.
- A Dance with Dragons, Chapter 28, Jon VI.
- A Dance with Dragons, Chapter 31, Melisandre I.