Meg had the rare privilege of becoming the grand torturer of Hell, Alastair's, pupil. She studied the art of torturing under him and became quite resilient to pain herself, as she merely joked around while being tortured by the demon possessing Christian Campbell, and managed to withhold information from Crowley despite suffering torture under him for more than a year. She was also capable of surviving holy fire after Castiel threw her onto it.
Presumably, Meg served as Alastair's pupil after she was exorcised by Dean Winchester. Prior to this, Meg did not show much resilience to pain and was said to have suffered greatly in Hell, a suffering which drove her to escape with a thirst for vengeance, with Azazel's plan seemingly forgotten.
Meg was a loyal servant of Azazel, who regarded her as his "daughter". From the moment of her debut, Meg served her "father" to the best of her abilities, and did not fail a single mission until she was exorcised by Sam, Dean and Bobby Singer.
It is unknown how they met, but they were close, as Azazel even took Meg to Lucifer's Crypts, a special location only very few, if any demons, knew about.
After her exorcism, Azazel bore a noticeable amount of resentment towards Dean and did not want to save him from his coma even as John was offering his own soul in exchange. Azazel saved Dean anyway, and dragged John to Hell where he was supposed to break the first seal binding Lucifer.
It is unknown if Meg was able to meet Azazel again before Dean killed Azazel with the Colt. Having suffered greatly in Hell upon being exorcised, Meg returned with the sole desire to punish Dean for what he did. Her alliance with Azazel appeared to have been forgotten as she used Sam as her vessel to convince Dean to kill him, despite likely being aware that Azazel needed Sam alive for his ultimate plan.
Upon her third return, Meg did not mention Azazel again and devoted all of her loyalty towards Lucifer, whom Azazel himself was also fanatically loyal to.
The only time Meg spoke of Azazel after his death was when she mentioned the Crypts, since Crowley was desperately trying to get the location out of her but she refused, giving it instead to the Winchesters. It is safe to say that Azazel, on the other hand, did care deeply for his daughter, but he was more obligated to complete his mission than to watch over her.
Meg was one of the very first demons to openly defy Crowley when he rose to power and became the King of Hell. She went as far as to side with her former enemies the Winchesters in order to foil all of Crowley's plans. Her efforts proved useful and it earned her increasing trust from Sam and Dean, while Crowley became increasingly unsatisfied with the lower-rank demon.
Meg's desire to upset Crowley led her to help the Winchesters infiltrate Crowley's prison where he kept various monsters. It was a promise from Sam that she would be able to torture Crowley that drove her to do this, and while she only managed it for a short while, Meg never sided with Crowley and remained an ally of Sam and Dean.
When Sam and Dean summon Crowley for his blood as part of a weapon needed to kill Dick Roman, leader of the Leviathans, Meg was reluctant to stay behind after spending some time watching over Castiel. When Crowley did appear, he promised Meg suffering and torture once their latest enemy was defeated. Crowley was able to make true to his word when, after Dick was defeated, Crowley managed to kidnap Meg and keep her prisoner.
Meg was tortured for more than a year, both out of pure distaste from Crowley and due to Crowley's desire to locate the angel tablet, the location of which Meg knew. In defiance, Meg never told her captors the exact location, only giving vague clues but provided the exact spot when the Winchesters finally rescued her.
Nevertheless, Crowley would also come to find the right location and confront Meg for the last time. To ensure the Winchesters and Castiel could get away with the angel tablet, Meg tries to attack Crowley but proves too weak to beat him, yet she provides her allies the right amount of time, and her final words were a mockery to Crowley's failure in getting the tablet.
Crowley's final punishment was to stab Meg with an angel blade, killing her.
Meg and Dean WinchesterEdit
Meg first encountered Dean when the latter accompanied his brother to a bar in Chicago, the two trying to investigate a case Meg had set up to ensure the brothers and John did not find the Colt. Meg did not wish to speak with Dean and tried, not for the first time, to bond with Sam. When she was forced to acknowledge the elder Winchester, she berated him for dragging Sam along wherever he wanted instead of setting him free.
This convinced Dean that Sam had been complaining about him behind his back, which was part of Meg's plan to tear the brothers apart. Unfortunately, the two brothers remained together and continued their investigation, during which Meg sent daevas after them. Once Meg captured them, she revealed her plan to lure John Winchester to their location. Both Dean and Sam were convinced she was merely working for the demon and not a demon herself. While Meg was distracted, the brothers managed to free themselves and throw her under the mercy of the daevas.
Meg returned to obtain the Colt once the Winchesters got their hands on it. After John provided her and Tom with a fake, Meg tracked down Sam and Dean in order to retrieve the real one. She went to Bobby's house but was tricked into a Devil's Trap. Dean began interrogating her for his father's location, but Meg merely lied about John being dead until the exorcism proved too painful for her to bear. Despite her confession, the brothers sent her back to Hell where she suffered great torment.
This drove Meg to seek vengeance. Meg returned some months later and took possession of Sam. She pretended to be him in hopes it would drive Dean to kill his own brother, but Dean was able to discover the truth in time and exorcise Meg once more. During her absence, Meg seemed to have mellowed and was not as vengeful as she was before, yet her desire to see Sam and Dean dead remained the same, a desire that had existed since around the time of her debut.
Meg re-encountered Dean shortly after Lucifer escaped his prison. Meg had Bobby Singer possessed by a minion and once the demon revealed itself, Meg sauntered into the room to greet the hunter. Dean was unfamiliar with her new vessel and mistook her for Ruby, until Meg urged him to think back further and Dean instantly felt disgusted to be in her presence again, glaring at her as she gloated about a dream coming true for the demons. She also was pleased with the chance to finally kill Dean, since he had an important role in the Apocalypse. Meg then kissed Dean rather roughly, to his disgust before she ordered the demon possessing Bobby to kill the hunter once and for all.
This plan failed when Bobby himself killed the demon, enabling Dean to fight Meg's other minion while Sam walked in just in time and fought Meg. Once Dean killed the minion with the Demon-Killing Knife, he posed to kill her too but Meg fled her vessel.
Meg returned a year later with an offer to help the brothers defeat Crowley. Dean also saved her from his demon possessed cousin. Her assistance led to the death of a handful of hellhounds, though Crowley survived the ambush at his prison due to Castiel's help.
In Season 7, Meg returned again after hearing news that Castiel, thought dead, had returned under a new name. Meg tracked the angel down to Dean, who she saved from a demon attack. Despite Dean not like having her around, Meg insisted he join forces with her against Crowley by reminding him of her helping him. Dean reluctantly agreed, and very soon he and Meg helped Castiel in remembering who he truly was. After Castiel became insane after taking in Sam's hallucinations, Dean begrudgingly allowed Meg to become Castiel's unofficial caretaker.
Relations between Dean and Meg remained sour yet their partnership stayed, due to their mutual dislike in Crowley. Their past conflicts appeared to have been shoved under the table in order to deal with more pressing matters, such as the Leviathans. Meg was ultimately captured by Crowley while Dean was sent to Purgatory with Castiel, and the two did not meet again until Meg was freed from captivity by Sam and Dean, more than a year later. Meg was annoyed that they didn't try to find her, despite her help.
Once again, Meg offered the brothers her help by providing information about Lucifer's Crypts, enabling the brothers to retrieve the angel tablet before Crowley could. To this end, Meg sacrificed her life, choosing her former enemies over her new King who was the one to kill her. It is unknown what Dean thought of her death.
Meg and Meg MastersEdit
The human Meg is the first known vessel used by the demon. From the moment of her debut, the demon used this human's name as her own, even though the demon also had other names. Most people only ever refer to her as "Meg". When posing as a nurse, the demon also used the surname "Masters".
What is clear is that the demon Meg does not care for her former human host, as she had forcibly taken possession of her while she was still in college and by doing so, put the human Meg's life in danger. When demon Meg was successfully exorcised by hunters Sam, Dean and Bobby, the human Meg died of wounds the demon sustained during possession, meaning the human Meg was kept alive solely because of the demon.
To make matters worse, upon seeing her corpse, Meg Masters' little sister committed suicide out of grief, something Meg's ghost informed the hunters who once saved her when she came back as a Witness.
A poor relationship between a demon and its host is not unique between the two Megs, and very few, if any demon truly cares about its human host, and is more fascinated in the host's appearance than the host itself. The demon Meg was said to have cut her host's hair short and dressed her "like a slut".
Meg and Tom both served under Azazel and were equally regarded as his "children", which made the two of them "brother and sister". While the two did well as a team, they did not seem to get along with each other.
A notable example was in "Salvation", when Tom decided to test if the Colt they received from John was real or not by shooting Meg in the chest. Although Meg did not die because the Colt was indeed a fake, had it been real, Tom would have killed Meg.
Aside from assisting their father in capturing John, the two were not shown to interact much. Tom's few appearances makes it impossible to know anything about their history. What is obvious is that Tom does not care for Meg while Meg's opinions of Tom are most likely negative given how angry she was when he shot her.