Supernatural season 14 has confirmed a sinister theory regarding Lucifer and his vessel that alters the context of the devil's debut appearance on the show. While Lucifer himself has been absent thus far in Supernatural's current season, the actor famous for playing him, Mark Pellegrino, has not been. This is because, for the first time in quite a while, Pellegrino is portraying Nick, the poor man Lucifer possessed in season 5 and has been using as his main vessel ever since.
Nick was first seen in Supernatural grieving the loss of his wife and child, a sadness that caused the man to fall victim to Lucifer's manipulation and accept the devil into his body. After years of possession, Nick was rescued by the Winchesters after Lucifer's defeat in the season 13 finale, but instead of relishing his second chance at life, he immediately returned to the same state of grief he was languishing in before and set out on a mission to discover exactly who was responsible for his family's unsolved murders. However, as Nick's quest to unravel this mystery intensified and was cemented as the B-plot of Supernatural season 14, it became clear that there was indeed more to Nick's backstory than viewers had been told previously.
Supernatural's demon lore has long held that humans have different levels of suitability when it comes to being the vessel of the devil. Sam Winchester was raised to be Lucifer's ideal host - the body in which his full satanic power can be unleashed. Most of the human population are on the opposite end of the scale and will explode before Lucifer even has a chance to pick out some new furniture. Somewhere in the middle are people like Nick, who can comfortably house Lucifer for longer periods of time and allow him to tap into a fair deal of his power.
Until recently, it was thought that Lucifer selected Nick as his vessel both because he was one of the few people who could contain him and because the recent murder of Nick's family made him easier to manipulate. Supernatural has now confirmed this not to be the full story. When Nick left the safety of the Winchesters' bunker to find answers, he was under the assumption that the man responsible for killing his family was some kind of crazed murderer that had escaped police detection. It really shouldn't have come as a shock to Nick when he later discovered that there was a supernatural element to the crime...
Nick learns that the man who killed his wife and child was possessed by a demon named Abraxas and after finding and interrogating said demon, it transpires that the order came from none other than Lucifer himself. Indeed, Abraxas claimed that Lucifer picked Nick as a vessel more or less at random and had his family murdered so that Nick would be more accepting to the idea of possession.
While it's possible that Abraxas was lying (that is what demons do, after all), it makes perfect sense that Lucifer would set up Nick's tragedy himself. Aside from all the inherent evil and taste for death that presumably comes with being the devil, it was arguably always too much of a coincidence that Lucifer would come across such a suitable vessel during such a dark and vulnerable period in their life. The reveal that Lucifer himself orchestrated this scenario makes Nick's possession far less coincidental and is also in keeping with everything viewers know about Lucifer's character.
For those very reasons, many Supernatural fans have often speculated over the last decade that there was more to Nick's situation than first met the eye. One popular theory suggested that Nick had killed his own family all along, and that the evil inside of him made Nick attractive to Lucifer as a potential rental property (Mark Pellegrino himself debunked this theory at a convention last year). The second major theory was that Lucifer himself had been behind the whole thing, just as he had organized the rearing of Sam Winchester as his ideal vessel. Now proved correct, proponents of this idea will likely be feeling very smug in the wake of Supernatural's latest offering.
Supernatural season 14 continues with "Prophet and Loss" January 31 on The CW.