Klaus Mikaelson's (Joseph Morgan) hybrid curse, eventually broken during the series, plays a central role in the events of The Vampire Diaries. Klaus is a member of the Original family. In the Middle Ages, when werewolves begin terrorizing the village the Mikaelsons live in, Klaus's mother Esther Mikaelson (Natalie Dreyfuss)—a witch—casts a dark magic spell that turns Klaus and his siblings into the first vampires. Unlike the rest of his family, Klaus is also placed under a second spell called the hybrid curse. This curse drives his character arc throughout The Vampire Diaries and The Originals.

https://screenrant.com/the-vampire-diaries-klaus-hybrid-curse-broken-sacrifice/