Doppelgängers, also known as Shadow Selves or Mortal Shadow Selves, were a supernatural occurrence that were created by Nature. Stefan Salvatore and Tom Avery are Silas' doppelgängers while Tatia, Katerina Petrova and Elena Gilbert are Amara's.
7 Silas. Silas originated the doppelganger bloodline that led to Stefan Salvatore. Silas pledged his love to Qetsiyah to gain immortality and became the first being of his kind. Bonnie and Jeremy discovered Silas's body with the Cure, but Katherine interfered and left Jeremy bleeding so that Silas could feed off him.
SilasSilas was the one who created the immortality spell 2000 years ago however, as nature creates a balance for everything, it created a version of Silas that could be killed, a shadow-self which ends up being Stefan. Silas then locks Stefan into a vault and drowns him in the river.
Julie Plec confirmed that Klaus is the origin of the bloodline Stefan, Damon, Caroline and Elena are from. It is possible to unlink a vampire from their bloodline using magic.
Katherine and Elena were the first doppelgangers introduced on the show, but they weren't the last. During season 3, Klaus and Elijah Mikaelson mentioned the first Petrova doppelganger, Tatia. The season 4 finale ended with the revelation that Stefan was also a doppelganger.
She was the biological daughter of John Gilbert and Isobel Flemming, and was therefore a descendant of Katerina Petrova, to whom she bears a striking physical resemblance. Elena is the the third and also the final descendant and doppelgänger of Amara, the originator of the Petrova doppelgänger bloodline.
Devil's curve is known as the curve defined on the Cartesian plane, which can be expressed in the form of an equation. Understood and presented by Gabriel Carmer, this is also known as his best works on the topic of determinants that resemble the two hyperbolic branches.
The difference between a resource and a capability is: a resource is a productive input or competitive asset, while a capability is the capacity of the firm to perform some internal activity competently.