This isn't technically the first appearance of Venom as a character, however the black suit which would eventually come to be Venom first appeared in the Marvel crossover series "Secret Wars" in 1984 to 1985.

Jumping a couple of years into the future, Spider-Man split off from the black suit in which in then bonded to Peter Parker's (Spider-Man) rival Eddie Brock in Spider-Man #300. Throughout the story, we only see glimpses of Venom attacking Peter's allies and even trying to kill him by pushing him in front of a train. It isn't until the end of the issue where we get a full glimpse of Venom's design. He isn't as vicious or beast-like in the ways that his later designs would show. He looks more like a dark reflection of spider man, which is what the purpose of his character was at the time. 

Venom originally was supposed to be a one-off villain. However, he was an instant success and became a fan-favorite character. This led to multiple story lines including him as a main antagonist. However, the early 90s led to a change in not only Venom's character but comics in general. The 90s created led to the creation of newer, edgier characters. Anti-heroes, or characters that do the right thing with more morally ambiguous methods like killing people became more popular. This led to a rise in popularity for characters like Wolverine, the Punisher, and of course, Venom. Venom eventually forms a truce with Spider-man and gets his own series with the most 90s moniker ever, the "Lethal Protector". This series began Venom's saga as an anti-hero, even teaming up with Spider-man in his first standalone series. With the change of the status quo in the 90s, Venom also gained a new design that helped personify this change. He gained his now infamous tongue and sharp teeth. His eyes also became more jagged and he began to resemble Spider-Man much less, coming into his own as a standalone character. 

To solidify Venom's change in character and further add to the 90s edginess, a new villain was created, Carnage. Carnage was meant to be a less sympathetic and more insane version of Venom, he also is what led to the aforementioned truce between Spider-man and Venom. This artifact's importance stems from the Maximum Carnage storyline and shows a solidification in Venom's change morally, rather than aesthetically. This storyline specifically, helped solidify a new villain and a replacement in a way for Venom. He eventually becomes like an archenemy to Venom and therefore he was able to grow into more into an anti-hero rather than a villain. 

During the early 2000s, Venom didn't really have any standalone storylines. Instead, the marvel writers changed who wore the suit to another spider-man villain and put him on a team of supervillains that served kind of like the avengers called the Thunderbolts. Essentially, they were a bunch of supervillains who were trying to be good guys, at least for the press. If they were the avengers, Venom was like the Hulk for the team. Following the early 2000s status quo for comics, the story incorporated more adult themes and drama, basically it explored the marketization of heroes and if superheroes were concerned with their public image than doing the right things. It was essentially just The Boys but not as dark and made by Marvel. This version of Venom is definitely the darkest by far. So something that some of the stories in the 90s Venom would often threaten to "Eat your brains!" Kind of like an edgy threat to make him seem cooler. However in a certain comic run called The Hunger he does in fact eat people because the suit craves a protein found in people's brains and in chocolate. While the first iteration of Venom was horrified of this, this new iteration did it constantly. Venom changed into a horror character and a true monster for the Thunderbolts team. This take on Venom fully embraced the horror elements, and made him more of a beast than a goofy spider-man villain with a cool suit. This also contributes to the trend of the 2000s; they aimed for a more gore and brutality evident in horror movies of the time such as Saw. The design embodies Venom's more primal look instead, as seen above he's much larger and looks more out of control. This design also includes the addition of beast like eyes inside the large white eyes he adopted from Spider-man. This design took Venom from super-villain to a monster out of a horror movie which is evident through his actions and design.

Now on a much lighter note, we change hosts once more. Following the early 2000s and going into the 2010s, comics went through a change once more. The popularity of the MCU and especially The Avengers led to yet another massive change in the status quo. It brought back comic popularity for a larger variety of people. The edginess of the early 2000s began to fade in popularity and Venom went through possibly the biggest change he's ever gone through. They changed the host once again to Spider-man's high school bully turned veteran and double amputee who struggles with alcoholism. The story was still adult and violent, however the demographic for Venom had changed thanks in part to a rise in popularity of shooter games and military action movies. The demographic for Venom was at the time, young adults and teenagers; and at the time Call Of Duty and other shooter games were at the height of their popularity. Therefore, following the market; Venom changed to Agent Venom. During this time, he was more of a hero than usual, yet another evolution. He became and avenger and wouldn't kill people unless absolutely necessary. This is a more controversial take on Venom for obvious reasons, however it is one of the most memorable changes in Venom's comic history.