Enzo (Michael Malarkey) has been around for a while, but not much is known about his backstory other than that he was an Augustine vampire.
Currently, Enzo's sole aim is to make Stefan's life miserable, and the last episode of the season will attempt to explain why he is the way he is.
Enzo's desire to make Stefan (Paul Wesley) suffer intensified after the younger Salvatore brother gave up trying to rescue Damon and Bonnie from the alternate universe they were trapped in. Enzo viewed this as a form of betrayal and vowed to make Stefan suffer as long as he lived. And one way to do that is by targeting the people Stefan loves -- namely his niece Sarah Salvatore.
And as part of his agenda, the previous episode saw Enzo revealing his vampirism to Sarah, and expressing his intention to integrate himself into her life so as to ruin her chances of leading a normal life.
Explaining why Enzo acts the way he does, Plec told Entertainment Weekly that his deep-rooted loyalty is a factor.
"Enzo's a guy who's deeply rooted in loyalty and we still haven't scratched the surface of learning why, what makes tick, why does he feel that way, why was Stefan's betrayal of Damon in Enzo's mind so profound that it makes Enzo want to go out of his way for sport to do things that will mess up Stefan's life," executive producer and showrunner Julie Plec said.
"One of the things that we do in the final chapter of this season … is to start exploring the backstory of Enzo and understand what makes him tick and why he is the way he is."
Meanwhile, the penultimate episode of season 6 is not expected to feature Enzo but the synopsis hints that Matt, whom Enzo has been using to get close to Sarah, will contemplate a major life change.
Elsewhere in the episode, Caroline will attempt to cope with her mother's death, and Kai will begin experiencing unexpected consequences from the merge and he will turn to Jo for help.
"The Vampire Diaries" airs Thursdays at 8 p.m. EST on The CW.