Nicolas, nicknamed "Nicki" by Lestat, is described as a tall man with dark wavy hair and dark eyes. He is a lifelong pessimist given to depression, in contrast to Lestat's generally enthusiastic and wildly cheerful outlook on life.
Despite his cynicism, Nicolas is still convinced that the Christian teachings are correct, and he cannot understand Lestat's unwillingness to believe. He delves deeper into his cynicism as his view of the world takes a darker turn. He claims that there is no good or evil, but rather only good or bad art.
Nicolas is crucial in explaining Lestat's later fixation with Louis de Pointe du Lac, whom Lestat cites as seeming "in his cynicism and self-destructiveness the very twin of Nicolas [...] Yet Louis gained a hold over me far more powerful than Nicolas ever had". In The Tale of the Body Thief, Lestat refers to Nicki as his former lover, indicating that the two shared a romantic relationship as mortal men.
Nicolas grows up in a small town in Auvergne, France, the eldest son of a draper. His family is respectably middle-class, and he is educated.
Initially, Nicolas meets Lestat when they are both children and are participating in an outing to "The Witches Place", a location where witches were burned at the stake in previous years. Lestat makes an impression on Nicolas when he begins to scream and cry during the outing. The two meet again as young men, after Lestat defeats a pack of wolves plaguing the village. Nicolas, acting as a spokesperson for the town, presents him with a red velvet cloak and boots lined with the wolves' pelts.
Nicolas is intrigued by Lestat, and requests to speak to him privately so that Lestat can tell him how he achieved the impossible. Lestat is not interested until he learns from his mother that Nicolas, like him, is a rebel. He has returned to the village because he is in disgrace: he was sent to Paris to study law at the Sorbonne, but instead fell in love with the violin, abandoned his studies and sold his textbooks to take lessons from Mozart. Although he has returned to the Auvergne, Nicolas has not given up his dream and continues to play his violin at home, prompting his father to threaten to break his hands.
Lestat seeks Nicki out at the village tavern, and the two quickly become inseparable; They have long, soul-seeking talks together, which they refer to as "Our Conversation". Eventually Nicolas and Lestat run away together to Paris. They find work in a small theatre on the Boulevard du Temple, called Renaud's, where Lestat begins acting, and Nicolas plays the violin.
When Lestat is kidnapped by Magnus and transformed into a vampire, he hides from Nicki, seeking to conceal his dark nature. He attempts to watch over Nicki from afar, sending him expensive gifts, such as a Stradivarius violin, and buying him a new apartment. Believing that Lestat has abandoned him in spite of the numerous gifts, Nicolas sinks into a deep depression. One night Nicolas senses Lestat nearby and plays the violin in an unsuccessful attempt to coax him out.
Shortly thereafter, Nicolas is abducted by a coven of vampires led by Armand. They feed from him yet do not kill him, and his mind snaps irreparably, plunging him into a darkness from which he does not escape. Lestat comes to the catacombs under Les Innocents, knowing that Armand has Nicolas, and liberates him after some difficulty.
Life as a Vampire
After being rescued and returning to Lestat's home with him, Nicki pleads to become a vampire. Lestat refuses, but is finally convinced to turn Nicki into a vampire. As Lestat feeds from Nicolas, he is plunged into the darkness in which Nicolas resides. He describes the scene as a seamless black sea, where all colours have faded, and that he sees only a bird soaring over the void expanse. He describes a feeling of having lost all that was once cherished. He describes it also as worse than his moment of darkness at the Inn, and tries to recoil from it. He finally turns Nicki into a vampire, which strains their friendship.
After the transformation, Nicolas becomes catatonic. Lestat and his mother Gabrielle take Nicolas to Paris, where he slips from their grasp and disappears into the night. Lestat cannot read Nicki's mind, but Gabrielle can, and tells him that the only things Nicolas thinks of are the funeral pyre under Les Innocents, upon which he was almost killed, and Renaud's theatre. They deduce that he must have run to the theatre and they find him there, sitting alone. Lestat gives the violin he had retrieved for him and Nicolas begins to play, improvising dark and terrible music. Lestat describes the music as "the darkness exploded, the darkness molten" and is horrified by it.
The remaining members of Armand's coven appear and begin to dance, and Nicolas joins them. Nicolas finally becomes vocal, and he demands the theatre, slinging insults at Lestat and finally admitting that he never wanted them to succeed in Paris. Nicolas proclaims his group to be the Theatre of the Vampires, and becomes the troupe's playwright and composer.
Lestat grants Nicki his wish and turns over the theatre. He and Gabrielle decide to leave Paris and leave Nicolas in Armand's care. The coven attempts to care for Nicolas, and Eleni refers to him fondly as "Our Divine Violinist", but he becomes progressively more insane and difficult to deal with, accosting strangers on the street and making no attempt to conceal his vampiric nature. Armand finally resorts to restraining him in a cell and cuts off his hands to prevent him from playing his violin so manically. Once released, Nicki writes a stack of new plays, then demands that the coven build him a funeral pyre and hold a sabbat, else he set fire to the theatre and kill himself there. The coven abides by Nicki's wishes and organizes a sabbat for him, where he dances into the flames, committing suicide.
Nicolas's prized Stradivarius violin, as well as an account of his death, are sent on to Lestat. He keeps the instrument with him and in the later novel The Queen of the Damned plays it for Akasha. Centuries later, during Lestat's journey to Heaven and Hell, he is unable to locate Nicolas in either realm.