Lilith

Lilith is a powerful demon and Lucifer's second-in-command. She was the very first human to be turned into a demon. In fact, she was the very first demon that Lucifer ever created after Michael cast him out of Heaven and was thrown into Hell. Lucifer twisted and warped her soul as a way to mock God's most beloved creation, humanity. She is feared and ruthless. Though, she prefers her hosts to be young girls, she's been known to possess beautiful women in order to fool or seduce men. As she was the first demon created, she therefore became the final seal to release Lucifer from his prison in Hell.

Background
Prior to the start of the series, a Crossroads Demon would cross paths with Bela Talbot. The demon made a deal with Bela: the demon would kill Bela's parents (Bela's father being abusive and her mother pretending that everything was fine) and guarantee Bela a large inheritance from their deaths in exchange for her soul ten years from the day they made the agreement. In the end, it would be Lilith who would hold this contract, amongst others.

Season 3
In "Jus In Bello", it is revealed by Ruby that Lilith is the one that sent a horde of thirty demons to kill the Winchester brothers after they are captured by Special Agent Victor Henricksen and being held in the local sheriff's office. Ruby further explains that Lilith is more interested in killing Sam due to the fact that she sees him as competition. After the Winchester brothers successfully defeat the horde of demons and Henricksen lets them go, Lilith makes her first appearance. She arrives at the sheriff's office possessing a little girl accompanied by an adult woman, most likely possessed by a demon. Lilith walks over to Nancy Fitzgerald, the secretary of the sheriff's office, and tells her that she's looking for two boys and that they're brothers, "one's really tall" and "one's really cute". Nancy asks what Lilith's name is. Lilith tells her that her name is Lilith and then reveals her white demonic eyes. Before, Nancy, Henricksen, or the deputy could do anything, Lilith raises her hand releasing a burst of white energy causing everyone in the sheriff's office to scream in agony. Later on, Ruby has the Winchester brothers turn on the news to see that Lilith not only killed everyone in the sheriff's office but blew up the building as well.

She then makes her second appearance in the season finale, "No Rest for the Wicked". She is shown to be on "shore leave", taking possession of a young girl and taking her family hostage in their home in New Harmony, Indiana. She forces them to treat her as their daughter, making sweets and deserts for her and playing with her, lest they should be killed for making her unhappy. The Winchesters track her down, and infiltrate the house, ready to kill the girl, only to realize that Lilith isn't possessing her. As the Hellhounds draw near to kill Dean, Ruby offers to keep them at bay with the knife, but as Sam hands her the knife, she reveals that she is actually Lilith. After the Hellhound kills Dean, Lilith tries to use her powers to personally kill Sam, but, to their shock, he is immune. As Sam charges to attack her, she leaves the body she is possessing and escapes.

Season 4
Lilith returns in the Season 4 episode as a hallucination that Dean has after catching a "ghost sickness" that plays on the victim's fears. Then later Lilith appears "The Monster at the End of This Book", this time in the body of a "comely dental hygienist", in order to seduce Sam into sacrificing himself and Dean in exchange for her stopping all of her efforts to break the 66 Seals. Later in the final episode of the season, Lilith waited at St. Mary’s Convent in order for Sam to kill her in order to break the last seal in order to release Lucifer free from his cage. When Sam actually did kill her, the blood spread around in a circle, forming a portal for Lucifer to emerge from.

Relationships

 * Lucifer (Creator, Leader)


 * Crowley (Second-in-Command, Lover)


 * Demons (Subordinates)

Powers
Lilith, being a white-eyed demon, is extremely powerful. She was one of the three whited-eyed demons that the Winchester brothers had ever seen, the others being Alastair and Crowley. Due to her being the first demon ever created by Lucifer she may have been the most powerful demon in existence until her demise at the hands of Sam. While she seems to be unafraid of normal angels, she has shown that she is afraid of archangels meaning that her power is nowhere near theirs. She has shown the following powers:
 * Demonic Possession


 * Telekinesis


 * White Energy Blasts


 * Granting Wishes
 * Control Over Hellhounds
 * Teleportation
 * Invulnerability 

Season 3

 * "Jus In Bello" possesses a little girl
 * "No Rest for the Wicked" possesses another little girl and the woman Ruby possessed

Season 4

 * "Yellow Fever" appears as hallucination
 * "The Monster at the End of This Book" possesses a dental hygienist 
 * "Lucifer Rising"

Pre-Season 4

 * Before "Lazarus Rising". mentioned to be in hell during Dean's hallucination