Jeff the Killer is a major icon in the Creepypasta world, rivaling Slenderman and The Rake as mascots of Creepypasta itself. It's just a shame the "original" story he came from is so, so horrible.
I'm putting "original" in quotes because the most famous story, the one written by an unknown author and published in 2011, is not the source of the character. The original character came from a short video called "Jeff The Killer" by a YouTube user named Seusser. Unfortunately, the account associated with that video has since been terminated (thanks, YouTube Heroes!) and is now considered lost media.
So, like many really, really shitty Creepypastas, the 2011 JtK story is just the author writing a bad backstory to something scary he saw on the internet. This is something people have done for Don't Hug Me I'm Scared, Username666 and tons of other stuff you've probably never heard of. Point is, it isn't original, it isn't good writing, and it sure as hell isn't scary.
It's very clear from the way the story is written that a child wrote it, and as such the protagonist (Jeff the Killer) becomes a teenager about the same age as the author. Jeff apparently has amazing kung-fu powers and can beat up bullies with one hand, and also wears cool clothes and apparently has superpowers despite the fact that there's otherwise no supernatural element in this story. But I'll talk a bit more about that later.
One of the story's biggest problems (possibly THE biggest problem) is the simplistic and juvenile prose. A container of bleach is described as a "thing of bleach." Some kind of strange, dark feeling in Jeff's brain is described as a "random feeling" three times in the same sentence. This story lacks very basic English and communication skills, and as such doesn't even feel like a real story. You can tell the author is trying their best, but that just adds to the problem. Jeff, a twelve-year-old with a public school education who is of otherwise average intelligence, often uses words like "illuminating" and "ominous." None of the characters talk like people, they talk like the author.
Another fatal flaw is that, despite the fact that there are only like five scenes, the story is extremely long. This story is about/over 3x the length of Candle Cove at least. Much of that time is spent on pointless filler, padding, or is just needlessly extended because the author struggles to explain very simple things.
The story suffers from another major flaw in that it's extremely cartoonish. Jeff punches a bully so hard their heart stops, the bullies skateboard everywhere they go and even hop over fences, despite living in a nice suburban neighborhood they apparently carry guns with them and shoot up a ten-year-old's birthday party, Jeff's face is mutilated by a "thing of bleach" and some fire, and the reason his face is mutilated is because he cut off his own eyelids and carved up his mouth, apparently without getting any kind of infection or bleeding out. All of this serves to make the story extremely unbelievable and contrived.
On another note, for a character who's supposed to be a Creepypasta legend, this story is amazingly low-concept. Despite being touted as a unique and terrifying serial killer, all Jeff manages to do is kill some bullies in self-defense and then his own parents. Aside from looking weird and threatening a little kid, he doesn't actually do anything impressive.
It is very clear that this is a story written by a child, and it's intended to scare other children. That would all be forgivable if the author hadn't blatantly stolen someone else's story and character and rewrote it to be about them. Jeff may be a popular character, and he's even appeared in much better stories since this, but the 2011 version of Jeff the Killer does not deserve to be remembered by the Creepypasta world, and it does not deserve to represent Creepypasta as a whole.
"Jeff the Killer (2011)" goes to sleep tonight with a thing full of bad writing and a 3/10.