It's easy to assume that the best supernatural beings on The Vampire Diaries did most of the killing, but the humans were in on it too. While most staking, decapitating, heart-snatching, and shooting was indeed vampire territory, mortals like Alaric Saltzman, John Gilbert, and Matt Donovan had plenty of blood on their hands.
Even the older humans in The Vampire Diaries, whom fans got to see in flashbacks, weren't afraid to kill here and there. This universe was a dog-eat-dog world, and everyone was in on the murder. The motive behind these kills differed from person to person, and there's even a serial killer in the mix.
Kelly Donovan - 2 Kills
An unlikely murderer, Kelly Donovan was quite irresponsible in her season 1 appearance. She was negligent and cared little about her kids or anyone else, and this latent tendency came through when Katherine brought her back from Hell to Mystic Falls.
Kelly came back to the town and killed off Trudy Sulez and another young man in order to keep herself alive and in the right dimension. However, Kelly didn't survive her new life for very long either.
Giuseppe Salvatore - 2 Kills
Damon and Stefan had the best brother moments and were the ultimate duo, but their own father hated them from the beginning. As seen in flashback, Giuseppe was an abusive man to his family, so he rarely showed love to Damon and Stefan when they were kids.
When Giuseppe found out that the brothers were consorting with Katherine, a known vampire, his anger knew no bounds. No familial ties mattered to him as he shot both his sons in cold blood, not realizing that they had vampire blood in them. Giuseppe turned them into the very creatures he detested by ending their mortal lives.
John Gilbert - 3 Kills
Learning she was adopted was one of the worst things that happened to Elena, and it deteriorated further when John Gilbert turned out to be her birth father. John also hunted vampires mercilessly, killing them even if they minded their own business and lived their lives.
John was responsible for three such deaths: his target was the tomb vampires who had come out into Mystic Falls, and he staked Pearl, her daughter Anna, and Harper in his absurd quest for justice. He was also pivotal in gathering up stray vampires and werewolves in season 1, who were burned alive by henchmen.
Samantha Gilbert - 4 To 6 Kills
In yet another trip to the past, fans met Samantha Gilbert, Elena's other bloodthirsty ancestor. A well-respected lady at first, she died one too many times wearing the infamous Gilbert Ring, which brought out a very dark side to her — serial killer dark.
She went on to become the opposite of a vampire hunter, killing Founder's Council members one by one. She almost decimated them in 1912, with Zachariah Salvatore being her primary victim, amongst at least three others. She also killed the Institution's guard and nurse, before taking her own life.
Alaric Saltzman - 8 Kills
It may have seemed like Alaric killed many more vampires and people, but his count settles at eight in The Vampire Diaries. He was one of the few vampire hunters who could be rational about wiping them out, and only did so if there was immediate danger presented from the vamps. Even then, fans found reasons to hate Alaric.
Alaric's first kill was newly turned Logan Fell, followed by two tomb vampires (one was named Henry). When the Gilbert Ring made him switch egos, he slew a medical examiner and Bill Forbes, who had vampire blood in his system
Pastor Young - 12 Kills
One of the most shocking moments on TVD was when Pastor Young conducted a council meeting in his cottage and deliberately caused a gas leak which blew everyone up. Everyone's deaths, including his own, were instantaneous and also a mystery — until Atticus Shane came into the picture.
He had been brainwashed by the creepy professor to sacrifice all of them, with the promise that The Other Side would be brought down and they will all return once Silas did. The event was tragic, and unfortunately the only thing Pastor Young would be remembered by.
Jeremy Gilbert - 5 (Seen), Countless (Unseen) Kills
The younger Gilbert always shared a conflicted relationship with vampires, and it truly came to a head when he became a Hunter. He trained himself and ended up killing two of Klaus' hybrids.
Jeremy's biggest kill was the permanent staking of the Original Kol. This naturally spurred the deaths of every single vampire who was related to Kol's bloodline, and that number probably goes into the upper thousands, if not more.
Matt Donovan - 9 (seen), C0untless (Unseen) Kills
Like Jeremy, Matt also came to abhor vampires. Even when he was supporting the Salvatores, Caroline, Bonnie, and Elena, he was actively killing vampires. Amongst ordinary vamps, Matt killed two street racers, and one in Doug's home with a well-shot wooden bullet. He also got rid of at least one, if not more, creatures from Julian's Army, and a minimum of one vampire from the Phoenix Stone.
Matt also shot and killed one human, his fiancée Penny Ares, even though that was a big mistake. Yet again, his most significant victim was Finn Mikaelson, whose death resulted in the visible end of Sage and Troy who were related to Finn by blood. Like Kol, even Finn had a massive number of vampires in his bloodline, all of whom perished when Matt staked him.