Most of the time, people look to heroes to take on the "big bads" of a comic universe. It's the natural order of things and typically, villains don't normally have their own villains. Unless, of course, the character in question is a former villain turned anti-hero like the Lethal Protector himself, Venom.
For the first half of his career, Venom was a part of Spider-Man's Rogues Gallery, battling the web-slinger every step of the way. After years of being the bad guy though, Eddie Brock turned to the life of an anti-hero and racked up quite the rogue's gallery.
Honorable Mention: Spider-Man
Truth be told, Spider-Man's not the typical choice for villains. After all, he's the web-slinging hero of New York, everyone's friendly neighborhood Spider-Man. And yet, his history with Venom can't be ignored.
Originally, Venom was only a symbiote attached to Peter as the iconic black suit. As time went on, the suit became more and more aggressive, causing Peter to "abandon" the symbiote and leading the alien to Eddie Brock. While Spidey's not technically a villain, from a certain point of view, he could be.
Lee Price
The list of heroes who have worn the symbiote over the years goes on and on, with the power levels differing depending on the character. For Lee Price, the low-level gangster who stole the symbiote off of Andi Bennet, Flash Thompson's friend, the power levels are close to none.
All Price really did was use the symbiote like a mind-controlling mask against criminals and heroes. When said heroes came together, not even a massive Venomized version of Price was able to stop Venom, Black Cat, Peter, and Flash from bringing him down.
Jack O’ Lantern
Every villain's got a gimmick. It can come in the form of a costume, a power, or even a weapon. For Jack O' Lantern, it was a combo of the latter two. From wearing a pumpkin to wielding toy-like weapons of mass destruction, Jack was a deadly foe for Venom and Agent Venom.
And yet, despite this, Jack was actually more a joke than a threat to Venom. Whether he was taking on Venom alone with his gadgets, assisted by a group of villains called the Savage Six, or even aided by a magic dream stone, Jack always lost pretty easily and faded into the background.
Sin-Eater
It's interesting how a character's life can be changed by one simple mistake. Before Venom, Eddie Brock was a reporter investigating a serial killer called Sin-Eater. Although he was told Emil Griggs was Sin Eater, Eddie was in fact wrong, and this accusation led to Griggs' expulsion and his run-in with Venom.
However, that ill-fated run-in wasn't the last Eddie would see of Sin-Eater. A copycat killer would appear and cause more chaos, hurting Eddies love interest Anne before the copycat's demise. In recent comics, Eddie even fought an undead Emil brought back from the grave.
The Life Foundation Symbiotes
Thanks to the Venom movie adaptation, fans know all about the mediocre villain known as Riot, another symbiote who fought Eddie and Venom. Yet, while Riot wasn't the best of villains, he was one of many other symbiotes known as the Life Foundation Symbiotes.
Considered to be the offspring of Venom enhanced by the Life Foundation and Roland Treece, the five symbiotes of Riot, Scream, Lasher, Phage, and Agony formed a vicious force for Eddie to take on and have since been a nuisance in numerous different forms.
Shriek
Love can come in many strange ways. As time has worn on, the likes of Frances Barrison went from being a drug addict to a super-powered villain equipped with supers-sonic abilities. Going by Shriek, Frances was freed during "Maximum Carnage" by Cletus Kassady.
Wreaking havoc on Eddie and his symbiote double time again, Shriek has become a nasty foe of the Lethal Protector and recently became a female version of Demogoblin, known as Demagoblin. Additionally, she has always committed herself to Kassady's cause.
The Jury
Funny enough, a lot of Venom villains end up being human characters rather than symbiotes. Venom's first comic book series, "Lethal Protector" saw the symbiote and Eddie Brock taking on the likes of a villain known as the Jury.
Led by General Orwell Taylor, whose son was killed by Venom during a prison escape, the Jury was a vigilante group tasked with taking down the symbiote. Armed with sonics, fire, and vengeance, the Jury ended up putting Spider-Man on trial before targeting Venom, although they would fail.
Scream
Out of all the Life Foundation symbiotes, the one who left the most marks on Venom is undoubtedly Scream. Originally using the body of Donna Diego as a host, Scream was one of the deadlier of the Life Foundation symbiotes and had a similar arc to Venom.
Starting out as a villainess using Diego's body, Scream would evolve over the course of comics from a killing machine to seeking redemption throughout several events. Although Donna was killed by Eddie, the Scream symbiote found new life later on in comics.
Toxin
While Eddie mainly wore the Venom symbiote, for a time, Flash Thompson wore the suit as Agent Venom. During that time, Eddie wore the Anti-Venom suit before having it cast off him and joining with the likes of the son of Carnage, coming to be known as Toxin.
Considered to be the strongest of symbiotes beyond Venom and its father, Toxin was a vicious and vile symbiote who rivaled Venom's previous veracity. Before Eddie was forcibly bonded to Toxin, Eddie battled Toxin multiple times and the brutal symbiote may appear in Venom 2.
Knull
Recent comics have shed a lot of light on Venom. Donny Cates run of the dark web-slinger has seen the symbiote gone from taking on guys like the Jury and Toxin to the god of symbiotes himself, the dark being known as Knull.
Sleeping within his own symbiotes on Kylntar (their word for cage), Knull was freed during the "King In Black" storyline and plagued Eddie throughout comics leading up to that final arc. A powerful god-like being who controlled the symbiotes and even slain Eddie, Knull is a dark and brutal Venom villain.
Carnage
There's really only one villain who can truly match the likes of Venom. During his first years as the symbiote, Eddie was locked in a cell with a dangerous serial killer, Cletus Kassady. When Venom broke Eddie out, Kassady's blood mixed with a part of the symbiote, merging with Cletus and giving birth to Eddies "son", Carnage.
In the years that followed, Cletus and Eddie have been stuck in a never-ending battle of blood, death, and symbiotes that has cemented Cletus as Venom's darkest villain who will be making his live-action appearence in Venom: Let There Be Carnage.