Kol Mikaelson is a major recurring protagonist villain and anti-hero/anti-villain of the second season of The Originals, as well as the main protagonist in its prequel webisode series, The Originals: The Awakening. He was also and anti-hero and antagonist in the Vampire Diaries series appearing in the third and fourth season.
He is portrayed by Nathaniel Buzolic and when possessing Kaleb, he is played by Daniel Sharman.
He is one of the Original Vampires and is the son of Mikael and Esther, the younger brother of Elijah and Finn Mikaelson, the older brother of Rebekah Mikaelson and the younger half-brother of Klaus Mikaelson. He was killed by Jeremy and Elena Gilbert to complete the Hunter's Mark on Jeremy. He temporarily came back to the land of the living when Bonnie lowered the veil to the Other Side.
Seeking revenge, he hunts down Elena as she assisted in his death, and attacks her, but is sent back to the Other Side when Bonnie puts the veil back up. His ghost was later seen on the Other Side, appearing to Matt after he temporarily died. He tells Matt the Other Side is being destroyed after Markos broke free. After Vicki is pulled into oblivion, Kol begs Matt to find a way to stop the Other Sides destruction, fearing what happened to Vicki will happen to him and all the other ghosts.
After coming back to life, this time possessing a witch named Kaleb in The Originals, at first it seemed as if he was helping his mother Esther with her plot but after meeting with Davina Claire and falls in love with Her, it is revealed that he has his own agenda as he plans on getting revenge on Klaus by making a White Oak dagger for him and what is quite ironic is that he allies with him, along with the other protagonist villains (Marcel, Hayley, Rebekah and Elijah) against Esther.
He wanted to make a White Oak dagger for Niklaus back in 1914 and he told Rebekah but she ratted him out to Niklaus, as a result, leading to his daggering so as vengeance, he had Rebekah possessed by a witch in an insane asylum.