Meg Masters (Demon)

Meg Master was a college student before she got possessed by a demon. After that, the demon she was possesssed by is now refered to as "Meg".

Background
Meg lived in Andover, Massachusetts until she was possessed by one of the demons. Much of her background is not known except that she left her family.

Season 1
She meets up with Sam for the first time in “Scarecrow” when she is on the roadside heading for California to get away from her family, or so she tells him. The two meet up again not too long later at a bus station and wait together for the bus to Sacramento to arrive. Sam tells Meg about Dean and how he seems to treat him like dirt.

After Sam leaves to help Dean, Meg kills a man in a van and ‘makes a call’ by slitting the man’s throat and draining his blood into a silver bowl. She refers to the person she speaks with in the bowl as her father.

We again met Meg in the episode “Shadow” where she is in Chicago at a bar. She tells Sam that California was not all it was made up to be, they decide to meet up later. Meg gives Sam her phone number, 312-555-0143 312-555-0143, and her last name, Masters. Sam later follows her to a warehouse where he finds her talking with something. Sam returns to Dean and tells him what he saw, they arrive at the conclusion that she was the one who summoned the Daeva (the evil of that episode), and she might have been talking with the Demon. Meg captures the brothers and reveals that their capture was a trap for their father. After breaking free, the Daeva sends Meg crashing out of a seven-story window to her apparent death.

However, Meg somehow manages to survive. We see her again at a church where she speaks with Pastor Jim Murphy, showing signs of being possessed, before she kills him. She later calls Sam and asks to speak to John. While on the phone, she kills a friend of John's, Caleb, and tells him that if he does not deliver the Colt gun to her by midnight in a warehouse in Lincoln, on the corner of Wabash and Lake, she would kill more of his friends. John agrees to the deal, despite how long it will take to get there. John makes it on time but gives her and her companion, Tom, a fake gun. Tom shoots Meg and reveals that it is a fake. Meg then takes John hostage.

In "Devil's Trap," Meg calls Dean to let him know she has John. Meg is both furious and anxious to obtain the Colt, and comes to a hunter and friend of the Winchesters', Bobby Singer's, auto shop where she confronts Dean, Sam, and Bobby. After presumably killing Bobby's dog, Meg breaks the door down and begins to taunt Dean and Sam about their father. Dean attempts to pour holy water on her, but is thrown backwards as Meg approaches Sam and Bobby. She unknowingly walks right into the center of a Key of Solomon, a magical circle which incapacitates any demons who enter. Dean then asks Sam to assist him with performing an exorcism on her while he tries to get information about their dad. They are able to get information on where their father is after Meg is seemingly in an abundance of pain from the exorcism. Breathless, she asks them to let her go, but to her surprise Dean does not free her from the trap. Dean then forces Sam to finish the exorcism on Meg, releasing her from the hold of the Demon's child that was controlling her. Upon the completion of the exorcism, the Demon's child flies out in a cloud of black smoke through her mouth and into the Devil's Trap where it is assumed to be destroyed. The true Meg reveals before she dies that the demon had possessed her for a year and that she was awake through some of it, referring to it as a nightmare.

The real Meg then feels the all of the pain that her body went through when the demon was possessing her, including the broken bones from her seven story fall and a gunshot wound to her abdomen. Slowly dying, she reveals where their father is in a cryptic message. Her last word was "sunrise", directing the brothers to the Sunrise apartments, where their father was held captive by demons.

Season 2
The demon that had possessed Meg has been in hell - which it describes, saying "It's a prison, made of bone and flesh and blood and fear". It has escaped to possess Sam, planning to kill hunters and try to provoke Dean into killing Sam. It no longer gives a "rats ass" for the plans of the The Yellow-Eyed Demon. While possessed by the demon Sam's smokes menthol cigarettes and drinks hard liquor. While in Sam's body the demon kills a hunter, Steve Wandell, and using Jo for bait nearly kills Dean. It goes after Bobby, but is revealed when Bobby gives it beer laced with holy water. Bobby and Dean trap it beneath a devil's trap, but they find it difficult to exorcise because it has used a spell to bind itself to Sam's body. Bobby finally burns across the binding brand, and the demon is exorcised.

Season 4
Meg is briefly resurrected when the "Rising of the Witnesses" seal is broken by Lilith in "Are You There God? It's Me, Dean Winchester". She goes after Dean Winchester and tells him how much she suffered because of the demon. She also mentions her sister committed suicide after learning about Meg's death. Dean manages to expel her for a bit by dropping an iron chandeller on her, causing her spirit to dispel. While trying to get rid of the witnesses, she goes after Sam and begins talking about what Sam is doing in the dark (demon blood). However, she is eventually put to rest by Bobby Singer.

Season 5
Meg returns, this time possessing a different human.

She is first seen in episode 1 "Sympathy for the Devil" She locates Dean and Sam after his freeing of Lucifer, she intends to kill Dean to prevent him from killing her "Father" Lucifer.

She also appears in episode 10 "Abandon All Hope..." and is in control of 8 or so Hellhounds, and sets them after the Group. She appears to idolize Lucifer, calling him father, and serving him loyally, when Castiel mentions the demon named Crowley, she calls him a traitor.

Season 6
Meg returns to her previous host, despite that she had been thrown into holy fire by Castiel. She and other Lucifer loyalists are being hunted by Crowley so she kidnaps Sam and Dean in order to force them to reveal Crowley's location. As Sam states, it was either "him or her."

Sam strikes a deal with her: she can torture and kill Crowley if Sam gets his soul back. Meg, the Winchesters and Castiel act on a tip from Samuel Campbell and locate Crowley's prison and infiltrate it, but are soon discovered by Hellhounds. Meg offers to hold them off and kisses Castiel, and gets an even more passionate kiss in return. When they separate, Meg is holding his Angel Sword.

She kills the Hellhounds with the weapon, but is then captured by a possessed Christian Campbell, who begins to torture her. Meg laughs at the pain, saying her host is a girl who moved to LA wanting to be an actress, and this probably wasn't even the worst thing to happen to her. While she is speaking, Dean kills Christian with Ruby's Knife. After trapping Crowley under a devil's trap, Meg tortures him to find out if he can restore Sam's soul. When he insists that he cannot, Dean hands the demon killing knife to her so she can kill Crowley, but he overpowers her and uses the knife to break the devil's trap. Castiel then appears with Crowley's bones, which he burns, killing Crowley. In the moment, Meg escapes before Sam can kill her.

Powers

 * Possession
 * Telekinesis 
 * Enhanced Strength
 * Arcane Knowledge - in Born Under a Bad Sign, the demon uses a spell to help break the Devil's Trap containing it. Also, in the same episode, it uses a binding link, a mark seared onto Sam's arm, preventing it from being exorcised.
 * Control over Hellhounds
 * Teleportation

Season 1

 * "Scarecrow"
 * "Shadow"
 * "Salvation"
 * "Devil's Trap"

Season 2

 * "Born Under a Bad Sign" possessing Sam Winchester

Season 4

 * "Are You There, God? It's Me, Dean Winchester" (the ghost of the woman she possessed)

Season 5

 * "Sympathy for the Devil" possessing a different body
 * "Abandon All Hope..." possessing this new body again

Season 6

 * "Caged Heat" possessing her new body again

Trivia

 * Meg is from Andover, Massachusetts
 * Meg has a sister who killed herself after her death.
 * Her phone number is 312-555-0143
 * Meg was possessed around October 2005
 * In 2.14 "Born Under a Bad Sign", the same demon that possessed Meg, possesses Sam. This demon is often referred to by fans as the Meg!Demon. When Sam is possessed he is referred to as evil!Sam.
 * The true name of the demon who posessed Meg has yet to be revealed. When asked by Dean in "Born Under a Bad Sign", he/she says s/he has lots of names.