Jason Harris hunted Stefan Salvatore, believing he had killed his sister, Joanne. However, he was mistaken as it was Damon, Stefan's brother, who killed her. Sadly, Jason shared an identical fate: dying at the hands of Damon.
Throughout The Vampire Diaries
Jason introduced himself on a video camera, giving the reason why he was hunting Stefan Salvatore: because he was the vampire who killed his sister Joanne. He went to Mystic Falls and in the Mystic Grill, he talked to a waitress about the Salvatore Boarding House. She told him that the owner Zach Salvatore had thrown everyone out and closed the boarding house three months previously due to the arrival of family (Stefan). Jason went back to his car and opened the trunk, checking to see if he had everything he would need: garlic, holy water and a crucifix.
Jason took his video camera and went to the Salvatore Boarding House and snooped around Stefan's bedroom. He put the crucifix in front of Stefan's door, garlic in his clothes and holy water on his bed. He found Stefan's journals and read a passage from one of them. He mistakes Stefan's writing about Elena and believed that Stefan was hunting her. He vowed he wouldn't let Stefan hurt anyone else and planned to kill him.
From in the bushes, Jason was shocked to see Stefan jump from the boarding house roof. He couldn't understand why his traps didn't work and why Stefan could go in the sun. He started to doubt whether what he believed was true until he came across rabbits drained of blood. He continued to search for more until he came across two dead bodies in the same condition as Joanne was found. He was horrified by the sight and knew he had to stop it.
He went back to Stefan's bedroom and found that it was still empty. He decided the only way to destroy a vampire was to destroy his home. He becomes spooked by a crow by the window and the window mysteriously opening. In the shadows there was a tall thin figure and Jason realized Stefan hadn't killed his sister, this vampire had! Damon grabbed him by the neck and raised him in the air. Jason dropped his camera while Damon dropped him. Damon picked up the camera and killed Jason.
Jason was a tall young man with short, brown hair and green eyes. He had an athletic build and in his appearances, he wore dark colored shirts.
- A Darker Truth (Part 1)
- A Darker Truth (Part 2)
- A Darker Truth (Part 3)
- A Darker Truth (Part 4) (Death)
- Jason is a common male name of Greek origin and means "healer". 
- Harris is a patronymic or paternal family name of British origins. 
- Part One
- Jason: Hi, I'm Jason Harris. (opens his laptop with pictures on the screen) This is Joanne, my sister. She had a neighbor, Stefan Salvatore, he's the one who killed her and I can prove it. That's why I followed him all the way from Manhattan... to here.
- Jason: So Stefan Salvatore as come home to his family. Funny, because Stefan Salvatore moves around a lot. I did some checking, Seventy times in the past forty five years. Only this is Stefan Salvatore--(shows a picture of Stefan on his phone). He's not old. He's a vampire.
- Part Two
- Jason: I'm in the Salvatore Boarding House. In a vampire's bedroom. The front door was open. Nobody's home. At least... nobody that can walk around in the day. And Stefan... he must be in the basement... in his coffin, which is good. It'll give me time to set up a couple of surprises for him... a few traps.
- Jason: (reads Stefan's journal) "I saw her again today, at her house... downtown with her friends... at the cemetery!" (throws the journal on the floor) I'm not letting him kill anyone else. When he comes outside... I'll be ready with this-- (holds up a stake). Ready...and waiting.
- Part Three
- Jason: (sees Stefan jump from the roof) Oh my God! He just jumped! Stefan Salvatore just jumped! No, flew! He flew, flew to the ground! (follows Stefan into the woods) But what about the garlic? The crucifix... or the holy water, even? I mean, how is he even out in the sun? Shouldn't he burn up in flames? Is this stake even going to work? What am I doing out here? Tracking down Dracula. Nothing makes sense. I know he killed my sister, I know he's a vampire. But if he isn't, then what?
- Jason: (horrified by the dead bodies) Oh God! It's the same! It's exactly the same way they found my sister! He's still here somewhere. I have to stop this.
- Part Four
- Damon: (chuckles evilly)
- Jason: (to Damon) You're not Stefan Salvatore, why are you in his room?
- Damon: Do you know it's rude to enter uninvited?
- Jason: Stay back! (Damon chuckles) You stay back! You killed my sister! (Damon chuckles evilly) YOU KILLED MY SISTER!
- Damon: (picks up the camera and points it at Jason) Say hi to the nice people of Mystic Falls... now, say goodbye. (turns off the camera)
- With confirmation that human souls are found in the dimensions, Jason either went to The Bright World or Hell.