The first demon was created by Lucifer, an archangel, after God banished him from Heaven for refusing to revere humans. In revenge, he took a human woman - Lilith - and stripped away her humanity to make her the first demon. For this offense, God commanded Michael to imprison Lucifer in a cage in Hell.
Demons have a belief system analogous to humans, according to the demon Casey, but while humans believe in God as their higher power, demons view Lucifer as theirs. No demon had ever actually seen Lucifer according to Casey, at least until that point in the show's progression. If this is true, it would mean Lilith was turned into a demon without seeing her maker.
All demons were once originally humans, who become demonic when tortured in Hell until their humanity is lost. Prior to becoming demons, it is unclear on what criteria the human spirits are judged as being worthy of Hell, other than selling one's soul to a Crossroads Demon or being a witch.
Demons usually do not have bodies of their own, except in the case of Acheri Demons, who can "manifest" as human children. Other demons appear as a 'black smoke' in their incorporeal form. Their presence may leave traces of sulfur. They manifest by possessing humans, alive or recently deceased, via Demonic Possession.
1st: Regular Demon
2nd: Crossroads Demon
3rd: Azazel, Yellow-eyed Demon
4th: Samhain, Demon of Halloween
5th: Lilith, White-eyed Demon
Exorcism will drive the demon from its human host and return it to Hell. A possessed human may incur physical damage while the demon is present, including fatal injuries, but will survive until they are dispossessed. A high volume of dispossessed individuals die; Dean commented that demons seem to enjoy wearing out their meatsuits. Humans possessed by demons exhibit black, red, yellow or white eyes depending on the demon involved.
Demons themselves, and people close to the gates of Hell, see the "real" decaying faces of demons, not just the body they use to walk the earth. It appears that angels can as well.
Demons' abilities and weaknesses vary depending on the apparent rank of the demon. Demons share many strengths and weaknesses with ghosts.AbilitiesAbilities
Telepathy and telekinesis - Demons can read minds. Some can influence an object's movement with their minds.
Superhuman strength and enhanced endurance - While hosting a demonic entity, a human's body can be made to perform extraordinary feats and resist damage. However, when the demon leaves, the host often dies of its injuries.
Seeing Reapers - Like angels, demons can perceive entities that are invisible to human beings, like Reapers.
Can resurrect or heal people, but only if a deal is made.
Capable of overpowering Alphas; a group of demons captured the Alpha Vampire on Crowley's orders, though only after it had been injected with enough dead man's blood to bring down a nest of regular vampires, and when they all attacked at once.
Mind control - Demons can influence and control the actions of human beings.
Pyrokinesis (known: Azazel, Brady; shown: Crowley)
Injury to humans by thought (shown: Azazel)
Destruction of objects with telekinesis (shown: Crowley destroys a light) and with the "Fiery White Light" (shown: Lilith, Samhein)
Overpowering or possessing reapers (overpowering: Alastair, possessing: Azazel)
Resurrecting people at will (Crowley, claimed).
Vulnerabilities & Preventative Measures
Preventing possession and location
Exorcism - When a demon is exorcised via ritual, it returns to Hell
Preventative Charms - After Sam is possessed, Bobby gives the boys charms to protect against possession.
Preventative symbol tattoos - Sam and Dean reveal that they have the protection symbol tattooed on their chests.
Hex Bags - Hex Bags can be used to help disguise and hide a persons whereabouts from demons.
Holy Water and Consecrated Ground - While most have some vulnerability to Holy Water, higher level demons, such as Lilith and Azazel, appear immune. Some demons are also able to enter consecrated ground such as churches, as shown by:
Salt - Most cannot cross a line of salt and they feel intense pain when they come in contact with it. Hunters use it in shotguns to wound them.
Iron - They cannot cross an iron line, and can be hurt with an iron rod.
Palo Santo - Burns in a similar way to Holy Water.
Devil's Trap - A symbol that is marked on the floor or ceiling that can trap a demon within it.
Means of Killing Demons
The Colt - the only method of permanent dispatch was to shoot them with the Colt and one of the original bullets. Bobby rebuilds the Colt with Ruby's help so that it can kill demons with new ammunition.
Knife - a knife that could kill demons, as well.
Angels - Angels have the power to kill demons with a touch.
Special children Powers - powers also allow him to kill demons.
Scythe: It is mentioned multiple times that Death's Scythe can also kill demons.
Burning earthly remains - Demons, like spirits, can be killed by burning the bones of the bodies they had as humans, before they became demons.
Spells: According to Ruby, there is a spell that can kill every demon in a one-mile radius that requires the heart of a virgin. As long as the meatsuits haven't been killed already, they will survive the spell. Demons can also be killed by a spell described in
the Seven Deadly Sins, who were released when the Devil's Gate was opened, possess humans and start killing people. Bodily contact with one of the demons appears to imbue the person touched with the sin the demon represents. Thus a family starve to death in front of a television (Sloth), Isaac drinks drain cleaner (Gluttony), while Pride confronts Sam and Lust tries to seduce Dean.
Envy possesses Walter, who is killed in the process, but is exorcised by Tamara. After Gluttony kills Isaac, his body is possessed by Wrath, but is immobilized by Tamara with a stake of Palo Santo. Sloth is trapped under a Devil's Trap and exorcised by Bobby, while Lust is subdued by Dean with Holy Water. Wrath and Lust are later exorcised by Bobby. Gluttony, Greed, and Pride are killed by Ruby with a demon-killing knife.
BLACK EYE DEMONS
These demons are the most common type of demons, but they are not a homogeneous group. They occupy positions on Earth and in Hell, as they are constantly being deployed and produced throughout Hell.
They appear to hold different ranks in demon society and display a range of abilities and powers. They are grouped together because when they possess a human, they can turn the hosts eyes entirely black at will. Most black-eyed demons serve a higher ranking demon or entity
A very powerful type of demon. Known white-eyed demons include Lilith, Alastair and possibly Samhain.
Crossroads Demons are entities that make formal agreements or bargains with humans, granting any wish in exchange for claiming their life and soul at a fixed point in the future. Deals made with humans are sealed with a kiss, and contracts are written invisibly on the skin of the person. They tend to have red eyes. When the person dies either before his or her time, or is killed by a hellhound at the end of the appointed period, his or her soul is sent to hell. Terms of the demonic contracts vary, but the person selling his or her Soul is usually given ten years to live after the deal is made.
A Crossroads Demon is typically summoned by burying a container of ritual items, including a photograph of the summoner, graveyard dirt, a black cat bone, and possibly yarrow at the center of a crossroads