Niruin (Skyrim)

Niruin is a Bosmer thief and a member of the Thieves Guild in Riften. He is a Master skill trainer of Archery.

Background
Niruin is originally from Valenwood, where he worked at his father's winery. As Niruin explains, he was wealthy, had many friends, and was betrothed to a beautiful woman. However, he found himself growing increasingly bored with his life. He secretly fell in with a gang called the Silver Crescents, but his father found out and gave him an ultimatum; leave Valenwood or go to jail. Niruin, who had made contact with Delvin Mallory while working with the Silver Crescents, asked to join the Guild and moved to Skyrim.

Location
Before being able to meet him, the Dragonborn will need to join the Thieves Guild. After the quest "A Chance Arrangement", talk to Brynjolf and do the "Taking Care Of Business" quest. Brynjolf will then ask the Dragonborn to follow him. Do so and enter The Ragged Flagon Cistern where Niruin can be found somewhere. Niruin is also possibly a part of a Companions quest, where the Dragonborn must rescue him from Morvunskar.

Trivia

 * When speaking with him up close, he appears to have fangs. Which possibly means he is a Vampire.
 * He could be part of the *Keerilth, a Bosmer clan of vampires from Valenwood indistinguishable from regular Bosmer unless you hold a candle to their face.