Nick

Nick was a solemn and lugubrious widower who lived in Delaware who became the primary vessel of Lucifer until he possessed Sam Winchester instead.

Early Life
Nick was married to a woman named Sarah, and together they had a child. One night, a criminal crept into their house and murdered Sarah and the baby in their beds. After the home invasion, Nick still resided in the house, and kept some objects that were connected to Sarah and the baby.

Season 5
In Sympathy for the Devil, Nick started hallucinating Sarah and his baby, and their blood. Lucifer appeared as his wife Sarah and told him that he was a vessel, and that Lucifer wanted his consent to possess him. Nick, believing it was a dream yet doubting it was, nonchalantly refused. Lucifer told him that he was misunderstood, that he was punished for "loving God too much". He promised Nick justice for his family. Nick consented to possession.

In Abandon All Hope..., Nick's body began to develop burn-like sores from containing Lucifer's essence. When Castiel mentioned the sores appearing on his vessel's face, Lucifer admitted that Nick was "wearing a bit thin."

In Hammer of the Gods, Nick's body had deteriorated further under the effort of containing Lucifer and massacring the Pagan Deities.

In Two Minutes to Midnight, Castiel told Sam and Bobby Singer that Lucifer would have to have been drinking gallons of demon blood in order to help maintain the integrity of Nick's body.

In Swan Song, Dean and Sam met up with Lucifer at an abandoned apartment in Detroit. Nick's body had degraded even further from the immensity of Lucifer's essence. Sam agreed to be Lucifer's vessel, and Lucifer then left Nick and entered Sam. Nick was seen motionless on the floor afterwards, and it is unknown whether he was dead, or alive but left catatonic by Lucifer. Given the condition of his body, he is likely dead.

Season 7
Although Nick doesn't truly appear in the season, Sam's hallucinations of Lucifer appeared in Nick's form.

Season 11
When Sam summoned Lucifer to talk to him about the Darkness, he manifested in the form of Nick despite having no vessel.

Later, inside Castiel's head, Lucifer took on the form of Nick again.

Season 12
In Stuck in the Middle (With You), while trapped within a small cage in Crowley's throne room, Lucifer manifests in the form of Nick.

In Family Feud, Crowley reveals to Lucifer that his demons found Nick's body a few years before and repaired and improved it so it would be "a fitting final home" for Lucifer. When Rowena MacLeod had cast Lucifer back into the Cage, Crowley perverted the spell so instead Lucifer was sent into Nick's body. Lucifer thanks Crowley, but wonders how Crowley really expects it to end.

Physical Appearance
Nick has messy, short blond hair and light blue eyes. He is six feet and one inches tall, making him shorter than Lucifer's true vessel, Sam Winchester, by three inches.

His usual attire consists of a green T-shirt, a dark green shirt hanging loose, blue jeans and dark shoes. Although he was wearing a white shirt and sweatpants when he assented to possession, Lucifer changed into this attire and continued to use Nick's guise when not occupying a vessel.

Season 5

 * Sympathy for the Devil
 * Free to Be You and Me (possessed by Lucifer)
 * Abandon All Hope...  (possessed by Lucifer)
 * Hammer of the Gods  (possessed by Lucifer)
 * Swan Song (possessed by Lucifer and corpse)

Season 7

 * Meet The New Boss (hallucination of him possessed by Lucifer)
 * Hello, Cruel World  (hallucination of him possessed by Lucifer)
 * Repo Man (hallucination of him possessed by Lucifer)
 * The Born-Again Identity (hallucination of him possessed by Lucifer)

Season 11

 * O Brother, Where Art Thou? (manifestation of him possessed by Lucifer)
 * The Devil in the Details (manifestation of him possessed by Lucifer)
 * Hell's Angel (manifestation of him possessed by Lucifer)

Season 12

 * Stuck in the Middle (With You) (body possessed by Lucifer)
 * Family Feud (body possessed by Lucifer)

Trivia
Nick
 * The name 'Nick' is possibly a reference to 'Old Nick', which is a nickname for the Devil.
 * When Lucifer is yanked from Castiel by the Darkness, his true form appears as Nick for a moment before he disappears.