Nick

"Take the bullet out of Lucifer's gun."

- Death talking about the usage of Lucifer's vessel

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

He formed a temporary physiognomy of Lucifer, but couldn't properly contain his strong essence. Lucifer's presence in Nick rapidly frayed his body.

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 resides in the house, and has kept some objects that were connected to Sarah and the baby.

Season 5
In Sympathy for the Devil, Nick starts hallucinating Sarah and his baby, and their blood. Lucifer appears as his wife Sarah and tells him that he is a Vessel, and that Lucifer wants his consent to possess him. Lucifer says he is misunderstood, that he was punished for "loving God too much". He says that he will help Nick get justice for his family. Nick assents to possession.

In Abandon All Hope..., Nick's body begins to develop burn-like sores from containing Lucifer's essence, and when Castiel mentions the sores appearing on his vessel's face, Lucifer admits that "Nick is wearing a bit thin."

In Hammer of the Gods, Nick's body has furher deteriorated under the effort to contain Lucifer and massacring the Pagan Deities.

In Two Minutes to Midnight, Castiel tells Sam and Bobby Singer that Lucifer would be drinking gallons of Demon Blood in order to help maintain the integrity of his vessel, Nick.

In Swan Song, Dean and Sam meet up with Lucifer at an abandoned apartment. Nick's body has degraded even further from the immensity of Lucifer's essence. Sam Winchester agrees to be Lucifer's vessel, and Lucifer then leaves Nick and enters Sam. Nick is seen motionless on the floor afterwards, and it is unknown whether he is 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 on the season, Sam's hallucinations of Lucifer appear in Nick's form.

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)

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)

Trivia
Nick
 * The name 'Nick' is possibly a reference to 'Old Nick', which is a nickname for the Devil.