Niklaus Mikaelson

Klaus is a vampire/werewolf hybrid and the primary antagonist of The Vampire Diaries television adaptation. He is half brother to Elijah, Finn, Kol, Rebekah, and Henrik.

Origin
A thousand years ago, Klaus and his family where mortals, save for his witch mother Esther. It is revealed his mother had an affair and Klaus's biological father was a werewolf. Esther put a spell on her family that turned them into vampires to protect them from werewolves. Klaus would have become a hybrid if not for the witches keeping his werewolf side in dormat. In retaliation, Klaus killed his mother, but became a target for his step father Mikeal, who began hunting vampires. To have his werewolf side released, a vampire, a werewolf and a Petrova doppleganger had to be sacrificed. In the middle ages, Klaus found Petrova doppleganger, Katrina Petrova, but she killed herself to become a vampire, rendering his ritual moot for now. Klaus then devoted himself to hunting her down.

Regin in Mystic Falls
In modren times, Klaus heads to Mystic Falls where found Katrina, now living under the name Katharine, and the next Petrova doppleganger, Elena Gilbert. He finds Katharine and tourtures her. Afterwords he finds the moonstone needed for the ritual, has a werewolf named Jules killed, turns Elena's aunt Jenna into a vampire for the ritual and abducts Elena. The ritual is complete but Elena doesn't die, turns out her father John Gilbert went through a spell to die in her place.

The next season Klaus sets out to create more Hybrids, starting with Tyler Lockwood. Klaus realizes that Elena needs to remain alive for him to make more Hybrids, so he decides to let her live, but has her vampiric boyfriend Stefan turn off his humanity. Eventually Klaus's siblings awaken, and Klaus kills his step father. His mother Esther is also ressurected. She has a plan to whipe out the vampire race by killing her children, a killing an original will whipe out the bloodline. Klaus and his siblings team up with the Mystic Falls Gang to combat Esther. Esther turns  the MFG friend Alaric into an original vampire but is killed by him. Eventually Klaus is subdued by a descection spell cast by Bonnie, but is now a target by Alaric. Klaus's body is staked, but Bonnie casts a spell to transfer Klaus's soul into Tyler's body.

Klaus goes bored and it's discovered dues to his werewolf genes his body didn't turn to dust. Klaus forces Bonnie to retransfer Klaus back to his original body. Once back, Klaus helps the MFG deal with the hunter Connor Jordan, who is eventually killed, meanwhile, Tyler plans the Hybrids to start a revloution against Klaus. In retaliation, Klaus kills his Hybrids and Tyler's mother. During the season, the main focus was to find a cure for vampires (doing so would awake the more ancient and powerful Silas), during so required a number of deaths, Klaus's hybrids including. Jeremy Gilbert, who became a vampire hunter, kills Klaus's brother Kol and his entire bloodline. Klaus swears revenge but is trapped in the Gilberts house by Bonnie. During this time it's revealed Klaus was in love with Caroline, Tyler's girlfriend. But Klaus breaks her heart by forcing Tyler to leave Mystic Falls with the promise to hunt him down. The cure is found but stolen by Katharine, nonetheless, Silas is awakened and heads to Mystic Falls. One of the first people Silas meets is Klaus, and Silas attacks him. Klaus is left wounded but it turns out the wound and the pain he was feeling was a hallucination, demonstrating how powerful Silas is.