Vampire

Vampires are magically reanimated human corpses which are inhabited by the spirits of the deceased person and who closely resemble the living human they were before their transformation. Vampires feed and survive on the blood of the living, typically on that of humans, and they can also transform other humans into more of their kind by sharing their own blood with them. Vampires are one of the many known supernatural species that were created by witches, albeit through the creation of their progenitors, the Original vampires.

Creation
A human who has consumed vampire blood in some way (whether by drinking it, having it poured into their open wound, or by being injected with it) and has subsequently died with the blood in their system will be magically revived as an undead vampire, just like the vampire who sired them. The exact nature of the human's death is irrelevant to this process; the only condition that must be met is that the body has to be more-or-less intact and able to function once they reawaken in transition, though the upper limits of physical damage upon a human body by which vampirism can recover has yet to be defined.

Sirelines
Every regular vampire who has ever existed is descended from those of their kind known as the Original vampires, who, unlike the majority of vampires, were turned not by dying with vampire blood in their system, but who were instead transformed using a spell that was cast using dark magic at some point around 1001 AD in what is now modern-day Mystic Falls. However, the ritual that resulted in their transformation does have similarities to how normal vampires are turned, in that they had to consume blood (in their case, the blood of the human Petrova doppelgänger Tatia which had been enchanted with an adapted version of The Immortality Spell by their powerful witch mother, Esther) before being killed while that blood was in their system.

After the Originals awakened in transition, they fed on the blood of another human from their village and were officially transformed into the world's first true vampires, from which all other vampires were created. Their blood possesses mystical properties that are passed down to each and every one of the vampires they sire, along with every vampire sired by their progeny, connecting all vampires to one of the six Original vampires from whom they are descending by a bloodline. Due to this link, the death of an Original vampire will result in this connection being severed, and every vampire in the deceased Original's bloodline will follow them in death within an hour. This bloodline connection can be broken, however. Using magic, Davina Claire and the the Sisters used a spell that Davina created to break the sireline of an Original in an attempt to free all of Klaus and Elijah's sirelings from their progenitors. This spell made it possible to kill an Original without killing their sirelings in the process. The spell was only performed on Klaus and it resulted in every vampire he or his progeny had ever sired to be free of their connection