Katherine Pierce/Stefan's Diaries

Katherine Pierce, officially known as Elena Delaney, is a recurring/main character in Stefan's Diaries series. She's the wife of Victor Delaney, and mother of Stefan Delaney.
==Early Life==
Elena Delaney, unbeknownst to anyone, is actually Katherine Pierce, who assumed Elena Gilbert's (her doppelganger and nemesis) identity after her timely demise. Since the deeds of Salvatore Boarding House were in Elena's name, she had no trouble claiming it and making it her home. She has been living there ever since.
Before that, Katherine was a vampire for over five centuries. But during a fight with Elena, she was force-fed the cure for vampirism, which turned her back to human. Since then she has been keeping a low profile, and trying to get used to being a human again.
Soon after that, she met Victor Delaney, a handsome and successful investor. They got married in the following years and had a son, who she named after her first true love, Stefan.
==Season One==
After an investigation, Stefan follows a hunch and ends up finding Katherine, who has been living in his old house with her new family, her husband and son, with the name of Elena. Only then Stefan discovers that Katherine had taken the cure for vampirism, which severed his sire link to Klaus and saved everyone in the bloodline after Katherine, enabling his and possibly other vampires' survival. Stefan agrees to keep Katherine's secret, and wishes her happiness in her life.
==Season Two==
The gang's encounter with Isla leads them to find out that she's not just a powerful witch, but also a vampire. Considering the possibility of involvement of doppelganger blood for such thing's creation, they reach out to Katherine, who reveals that she knows Isla.
After becoming a human after 500 years, Katherine had started aging rapidly. In desperation, she sought help from a witch, who claimed she could fix her, but in return she needed some of her blood. Katherine agreed, and Isla managed to reverse the aging and stabilize it, making her no different than a woman of her age. But in order to stay that way, the cure had to remain in her system, which means she had to avoid any kind of major blood loss for the rest of her life.
==Season Three==
After Silas takes control of Stefan and turns him against his friends, Katherine manages to bring him back by pretending to be Elena.
==Season Four==
Events in this season will force Katherine to reveal who she really is to her husband, which will create a rift in their relationship. 
in development
From that point on, the character is credited as Katherine Delaney.
==Season Five==
in development
==Season Six==
Katherine Delaney becomes a main character this season.
in development
==Trivia & Notes==
*Katherine is the only non-main character who appears in all seasons.
*Due to the time jump of 12 years, Nina Dobrev plays a character older than herself. Even though this originally triggered a search for an older actress, the idea was scrapped almost immediately because "no actress other than Nina can play Elena or Katherine".
*Aside from seasons Four and Six, Katherine appears once in every season. In season Four, she appears multiple times in recurring capacity, and in season Six she is upgraded to main cast.