Pestilence

Pestilence is the fourth and final of the Four Horsemen of the Apocalypse to be introduced on the show. Actor Matt Frewer is confirmed to portray Pestilence in Hammer of the Gods and Two Minutes to Midnight, where he will get his own debut like his three brothers: War, Death, and Famine.

Description
Pestilence first appears at the end of Hammer of the Gods, where he is portrayed as a disease-ridden old man driving an old green Ford Pinto Wagon with Nevada license plates that read "SIKN TRD" (sick and tired).

Like his three brothers, Pestilence's power is channeled and controlled by use of a special ring he possesses, and the only way to impede him is to separate him from this ring. As his name implies, Pestilence has power over anything that can inflict pain or misery on the Earth, such as infestations, plagues, and most prominently diseases. He is said to ride on a white horse, but as his brothers have all "gotten with the times", he is likely to travel in some kind of white automobile alluding to his association with the color white from Biblical lore. It is unknown how he will demonstrate his powers in Episode 20, though foreshadowing from "The End" seems to give a small hint at what Pestilence may do: the Croatoan virus, shown to possibly be Lucifer's endgame for the human race in "The End", most certainly falls under the power of Pestilence as it is a viral epidemic. Given that Pestilence makes his debut near the end of Season 5, this further adds to this possibility.

Hammer of the Gods
At a small drug store, a large fly lands on the clerk's desk as the clerk reads about a viral epidemic that has been going around the area, but before he can swat it, Pestilence enters the store, hacking and coughing up gobs of a disgusting mucus and spreading it all over everything in his reach as he looks for some flu medicine. When he takes it to the counter, he sneezes more of his mucus into the clerk's face, likely infecting him with the latest virus he has been spreading in the area. When Pestilence leaves the store, he gets in his sickly green beaten-up Mustang, tosses the medicine aside and laughs to himself as a swarm of flies fill his car all around him, revealing that his "illness" is merely a ruse so he can spread his diseases and infect as many people as he possibly can.

Like his siblings, he has been busy spreading his influence across the land, and according to the paper the clerk is reading, he has already spread several contagious diseases in the area. When in the disguise of an ill traveler, he tells the clerk he still has "a lot of driving to do", implying he has many more tricks up his sleeve.

The Devil You Know
Since the previous episode, the brothers have been chasing after him, always one step behind him. He has been causing mass outbreaks of the Swine Flu, something the brothers find strange because Pestilence could do much worse, such as the Croatoan Virus for example. It is revealed over the course of the episode that the Swine Flu outbreak is part of a bigger plan Pestilence is working that will eventually involve the Croatoan Virus. Having infiltrated a major drug company, his servant Brady and a few other demons have begun testing the virus on unsuspecting humans in the labs at night, with the eventual plan being to disperse the virus among regular Swine Flu vaccines to cause a mass outbreak.

Though not seen in the episode, Brady communicates with Pestilence through the use of an identical goblet filled with blood of a human victim, similar to the method used by the demon that possessed Meg Masters. While we do not hear his voice, several flies appear from the goblet, and Brady explains that the trials are proceeding as expected, but that they must be careful as to not arouse suspicion. Pestilence seems pleased with the news, but informs Brady that should he fail, he can always find another demon to replace him.

Two Minutes to Midnight
In the beginning of the episode, Pestilence is revealed to be hiding in a retirement home, posing as a "Dr. Green". He is seen examining an elderly patient, infecting her with various diseases and observing the effects they have on her before she dies. When he is alerted by a demon posing as a female nurse that the Winchesters are here, he decides to infect them with various diseases, despite the demon's reminder that Lucifer has ordered them not to be harmed. He greets the Winchesters as they stagger towards his room, suffering from Pestilence's powers and has the demon nurse bring them into the room. He goes on to tell them that he prefers diseases to people, and how he can't understand why God loves something so "messy and weak". As he moves in to finish them off, Castiel arrives and Pestilence is surprised to find that the low-powered angel is now succeptible to his powers. Despite his weakened condition, Castiel manages to cut off his ring finger and kill the demon nurse. As his powers begin to wear off of the trio, he says "It doesn't matter. It's too late," before vanishing.

Sam and Dean later learn that he referred to his and Lucifer's plan to spread the Croatoan virus through shipments of swine flu vaccine.

Family

 * Famine (Brother)
 * Death (Brother)
 * War (Brother)

Powers and Abilities

 * Immortality
 * Able to inflict plague and disease on others.

Season 5

 * "Hammer of the Gods"
 * "The Devil You Know" (Unseen) Brady commumicates with him through the goblet of blood
 * "Two Minutes to Midnight"

Alternative Titles

 * The Green Horseman of the Apocalypse

Trivia

 * Pestilence's license plate reads "SIKN TRD", which translates to "sick and tired".
 * His ring is solid silver with a sickly green gem in the centre.
 * Even though Pestilence is the White Horseman of the Apocalypse, he rides a sickly green "horse", which is generally supposed to be the Pale Horse Death is meant to ride, but instead Death rides the White "horse".