The Vampire Diaries mentioned Lily Salvatore, mother of Damon and Stefan, only in passing until Season 6. While she presumably died at some point in 1858, it was discovered that she was alive; however this wasn't good news for the Salvatore brothers, who were left dealing with the ramifications of this revelation. With this revelation, let's look back at how she went from gentle mother to a "new" woman with a "family" of her own.
As a Human
Born as Lilian on February 27, 1820, she married Giuseppe Salvatore, who was a cheating, abusive husband. Once, during Thanksgiving 1851, she tried to run away to New York with her sons and bought the tickets with the money she stole from Giuseppe, who beat Lily for trying to take his sons. He threatened she would never see her kids again if she made another attempt to runaway. In 1858, she suffered from tuberculosis and was sent to a hospital by Giuseppe, but Damon and Stefan weren't allowed to talk to her.
Becoming a Vampire
In the hospital, a vampire gave her their blood, turning her. While she did return to Mystic Falls to see her sons, Stefan's pulse triggered her bloodlust, so she left so before hurting her kids. Lily proceeded to go on a killing spree across Europe, with a death count of more than 3,000 people.
She soon met former members of the Gemini Coven, who had been cast out since they were siphoners, meaning they could only use magic after they drained it from someone else. While she eventually met young Valerie and Oscar, she would soon meet Mary Louise, Nora and Beau. During her killing rounds, she also met and fell in love with Julian, a charming vampire.
In 1863, she sent Julian and Valerie to check in on Stefan, but Valerie and Stefan fell in love, and Valerie got pregnant. Julian knew having a grandchild would tear Lily away from her new "family," so he beat Valerie till she miscarried. Valerie later committed suicide, unable to refute Julian's story that he found her beaten on the road. However, she died with Lily’s blood in her system, so she woke up as the first Heretic, a witch-vampire hybrid.
Later, Lily transformed the remaining five witches, with whom she planned to kill the Gemini Coven. While Julian was killed, his soul trapped in the Phoenix stone by vampire huntress Rayna Cruz, the coven sent the remaining vampires to the Prison World, where they were stuck in 1903 forever without any source of blood. Lily's family decided to give up their rations to keep Lily alive while they died.
Lily Returns to Mystic Falls
While trying to flee from Kai in the Prison World, Bonnie Bennett encountered Lily before escaping to Mystic Falls via a spell. On returning, she showed Damon a recording of Lily. Later, when Damon ran out of ways to turn on Stefan’s humanity in Season 6, he and Bonnie rescued Lily, tricking her into thinking that they would come back for her companions.
Coached by Damon, she managed to convince Stefan that she tried to come back for them but was imprisoned by the Gemini Coven. Her admission pushed Stefan to turn on his humanity, but when Damon and Bonnie went back on their promise of rescuing her companions, she lost her composure. This lead to her murdering many, attacking Bonnie and Elena and sparing Joe, who was pregnant.
She was later overpowered by Damon and Stefan and imprisoned; however, Kai rescued her and brought her family back from the Prison World. For their protection, she brokered a deal with Stefan. This meant Mystic Falls was vacated and given to her and her family so they could feed on anyone who crossed the town’s borders.
Julian's Return
While she had a strained relationship with Damon, especially after learning she prompted Kai to cast a sleeping spell on Elena, Lily bonded with Stefan. This bond was tested when she resurrected Julian via the Phoenix stone, so Stefan learned he killed his unborn child.
He tried killing Julian, but the older vampire was stronger and extremely manipulative. Julian convinced Lily to link their life forces, so her sons wouldn't kill him. Although Stefan told Lily what Julian did to Valerie, his true character came through when he got in a sword fight with Enzo, despite knowing every wound inflicted on him would harm her as well. His superfluous claim that he loved her reminded Lily of the abusive Giuseppe, allowing her to see Julian for the monster he really was.
She joined forces with her sons to convince her family to help kill Julian; however, Mary Louise helped Julian hold Damon and Valerie captive, forcing Lily to stake herself in hopes of killing Julian. This backfired because Mary Louise severed the link between them. Julian ran away while Lily started to die. Everyone said tearful goodbyes, but Damon refused to accept her apology. Lily was laid to rest near the Salvatore family plot.