Nighteyes is confident, sarcastic, and carefree. He remains energetic and playful even after he has grown from a puppy to an adult wolf. Because Nighteyes is a wolf, he experiences life in a fundamentally different way than Fitz. He lives in the moment, joyfully, and does not dwell on either the past or future. Nighteyes frequently disapproves of Fitz's emotional reactions and encourages him to embrace a more wolf-like attitude.
Fitz and Nighteyes meet when Fitz comes across a caged wolf pup in a crowded marketplace and purchases him, intending to release him outside of Buckkeep. However, the wolf refuses to return to the wild. Despite Fitz's reluctance to bond with another animal, he and "Cub" eventually form what becomes Fitz's strongest Wit-bond, and the wolf reveals that his true name is Nighteyes.
From then on, Nighteyes is a near constant presence, at Fitz's side and in his head, augmenting his senses and decision-making process with his own perception and opinions.
Nighteyes saved Fitz's life during Fitz's torture by taking Fitz's mind into his body, and letting Fitz's old body die.
Later, Burrich forced Fitz to return to his old dead body, and continue his life as a man. Fitz then leaves the name FitzChivalry Farseer dead and travels to beyond Mountain Kingdom.
Nighteyes accompanies Fitz on his travels after the events of Assassin's Quest.
After many years with Fitz, Nighteyes dies from wounds suffered from a battle with a mistcat.
Nighteyes' "spirit" remains as a companion to Fitz for a time, then transfers to appear as Bee's "Wolf-Father" and offer her support through her kidnapping and escape.
Nighteyes' spirit continues to advise and assist both Bee and Fitz throughout their struggles. As Fitz's death nears, Nighteyes finally convinces him to carve a stone wolf to hold the memories of Nighteyes, Fitz and the Fool forever.