Kol Mikaelson is portrayed by Australian actor Nathaniel Buzolic and was played by British actor Daniel Sharman while possessing Kaleb's body.
Kol is the youngest surviving son of the Original Family, since the death of his younger brother Henrik and the second youngest child still living, being older than Rebekah. He tries to kill Matt Donovan for entertainment during the Originals' family ball, but is stopped by Damon Salvatore.
In the season three episode, "Heart of Darkness", Kol appears in Denver, Colorado, where Elena and Damon had sent Jeremy, to get him away from Mystic Falls and protect his life. He threatens to hurt Jeremy, in order to prevent Elena and Damon from trying to find out the history of Damon's blood line; (if they managed to do so, they might find out that Elena's friends are not descended from Kol, which would allow them to kill him—see "Mythology" section). Damon drives a baseball bat through Kol's body in order to debilitate him so that he, Elena, and Jeremy can escape. Kol later appears at the house of Mary Porter, the vampire who sired Rose. Kol kills Mary, so that she is not able to tell Elena and Damon about the history of her bloodline, which could lead them to find out which Original vampire Damon, Stefan, Caroline and Abby Bennett are descended from; Mary sired Rose, Katherine Pierce forced Rose to sire her, and Katherine later sired Damon and Stefan.
In season four, Kol returns to aid Rebekah in finding the rumored "cure" for vampirism. He tortures Professor Shane, who supposedly knows how to get the cure. When Kol realizes that Shane plans to release Silas, the first and most dangerous immortal being of all time, Kol stabs Shane through the torso with a wooden object, killing him. However, Bonnie is able to save Shane's life through an "expression", or dark magic spell.
Kol compels Damon to kill Jeremy so that they cannot find Silas, but Stefan locks Damon away so that he cannot. Elena and Jeremy decide to try and kill Kol because he is trying to stop them from getting the cure. Since Jeremy needs to kill vampires to complete the map to the cure, they conclude that if they kill Kol, which also kills his whole line of vampires, the map will be complete.
Elena lures Kol into the house and waits for Jeremy to bring Bonnie, but he does not make it in time. Elena and Jeremy are talking later when Kol appears, storms into the house and tries to cut off Jeremy's hunting arm. Elena corners him and showers him in water mixed with vervain. Jeremy stabs Kol with the white oak stake and he dies. Meanwhile, Klaus is watching furiously in the doorway, unable to help his brother because he has not been invited in. He vows to avenge his brother's death, swearing to kill Jeremy, Elena and anyone else involved.
Kol returned in the season four episode "The Walking Dead", along with several deceased characters as ghosts, longing for revenge against their killers and the residents of Mystic Falls. He clashes once more Matt Donovan, wounding him by throwing a glass bottle at his shoulder and taunting his sister, angered at her brief grieving period, before proceeding to attack Elena, grieving for her brother at his grave. His neck is snapped by Stefan before he managed to kill Elena, however appears in the next episode, "Graduation", threatening Bonnie into completely destroying the veil so he could return to life. Bonnie plays along with his plan, however deceives him by luring him into a trap, so he can't cause any more harm until the veil is returned.
Kol later appears to Matt Donovan while Matt is temporarily trapped on the Other Side. After Matt witnesses his sister Vicky being sucked into oblivion, Kol reveals that the Other Side is unraveling, slowly taking one spirit after the other. Soon, every spirit of the supernatural kind will be gone. Kol begs Matt for his help, before he, too, will be swept away. However, upon awaking, Matt doesn't remember. Soon, the Other Side completely disintegrates, and Kol's fate is left unknown.
Some time later in season 2 of The Originals, a young man named Kaleb appears in New Orleans, flirting with the young but powerful witch Davina Claire. He later meets up with Cassie and Vincent, two witches whose bodies have been taken over by Esther and Finn. It's revealed that Kaleb is actually Kol, having taken possession of a body as well. Kol continues his relationship with Davina Claire, originally because his mother told him to but develops feelings for her. He chooses to side with Davina over his mother Esther who he helps stop along with his siblings. However, this leads to his brother Finn casting a spell on him which eventually kills him, leaving Davina heartbroken. In season 3 Davina works to resurrect Kol which she succeeds in doing by aligning herself with the Strix to get the power she needed. Kol is later resurrected by Davina through the energy that was used in un-siring Klaus.