Joseph Morgan as Niklaus Mikaelson

Niklaus Mikaelson (a.k.a. Nik or Klaus) is an Original/Hybrid, and the son of an unnamed werewolf and Esther. He has six half-siblings: a deceased unnamed older half-brother, four other half-brothers named Elijah, Finn, Kol, and Henrik, and a younger half-sister named Rebekah. Klaus is also the step-son of Mikael, with whom he had a strained relationship.

Klaus was born to Esther and an unknown man, in a small village that would eventually become known as Mystic Falls. Klaus has six half-siblings and a step-father named Mikael, a wealthy landowner who moved with his wife Esther to the New World after their home village was devastated by a plague. Klaus was close to his family with the exception of Mikael, who was inordinately hard on Klaus.

Many years before, his mother had had an affair with a man from the neighboring village, whose inhabitants were known to be werewolves. When Klaus' brother Henrik was killed by a werewolf, Esther performed a ritual which transformed Klaus, his siblings and his step-father into. Esther and Niklaus looks at Henrik's bodyvampires. When Klaus made his first human kill, his werewolf gene was activated, thus revealing Esther's infidelity. Mikael then hunted down and killed Klaus' father and his entire family, not realizing that doing so would ignite a war between vampires and werewolves that has been perpetuated across the ages. Soon after turning her children into vampires, Esther placed a curse on Klaus which forced his werewolf side to lie dormant, and then rejected and abandoned him. In retaliation, Klaus murdered his mother, and framed Mikael for the act.