Eddie Brock

Diagnosed with cancer, Eddie Brock went to writing to soothe his pain. As a reporter forthe Daily Globe, he wrote about the Sin Eater story. The villain was a killer who wanted to clear the city of sins. When he received a tip that a civilian might be the Sin-Eater, he printed it on the paper. This was a huge story at the time, as nobody knew who the bad guy was. Feeling proud of the story, he was brought back down to Earth when Spidey captured the real Sin-Eater. Brock went nuts and lost his job. Not only that, but his father Carol disowned him (again) and his wife Anne Weying left him. Everything was going wrong in his life. Having seen his uncle perish slowly from cancer, he knew he didn't want die that way; he decided to take his own life.

The symbiote's story is a long one. Having come from Planet X, a planet that was destroyed by Galactus, it fled to another one, a very special one. The planet was chosen by the omnipotent being known as The Beyonder to house the ultimate battle between good and evil. The being snatched heroes like the X-Men, the Avengers, Fantastic Four, Hulk and Spider-Man to fight against Dr. Doom, Galactus, Dr. Octopus, Lizard, Enchantress, Absorbing Man, Molecule Man, Klaw and many others. After a fight where Spidey's costume took a beating, he enocuntered several heroes which would produce a costume out of thin air if you thought about it. Spidey went to the wrong machine, and suddenly, the symbiote covered him and became the black costume. When the heroes had dfeated Doom, they all returned to Earth, and Spidey had his new costume with him. He wore it for several months, enjoying that it produced organic webbing and could mimic his civilian clothes. After talking to Reed Richards, Peter discovered that the costume was a living entity. Richards had the symbiote imprisoned, but during an attempt by The Trapster to infiltrate Freedom Plaza, the symbiote escaped. It attempted to force Peter to accept it again , but couldn't, so Peter tried to kill the symbiote by using the noise of a church bell tower. The plan worked and the symbiote saved the Wall Crawler's life before hiding itself in the church, waiting for someone to save itself.
Eddie Brock, fearing death, went to Church one night to ask the Lord for forgiveness for what he was about to do. Fate had brought him to the same church where Spider-Man had defeated the symbiote. The symbiote felt Brock's hatred towards Spidey and soon bonded together with Brock to became 'Venom.' Not only that, but being together caused Brock to receive an extension on his life due to the symbiote feeding on his heightened adrenaline (which it was attracted to in Spider-Man). However, if the symbiote ever left Brock to go back to Spider-Man, the ex-reporter would surely die from cancer.
While Brock wanted the symbiote, it only wanted revenge at Parker, and used Brock to get back at its former host. The symbiote fed on adrenaline, which Peter had a lot of whenever his spider-sense turned on, and Brock to (although, not as much) as a result of taking medication for his cancer. Brock has always known that the symbiote has been using him, which only intensifies his hatred towards Spider-Man.
Venom wasn't a hero or a villain, he was a vigilante. He would hurt or kill all those whom he thinks are guilty. He only hurt people who comitted crimes. He's never hurt anyone who is innocent. Venom strongly believes that Spider-Man is guilty for ruining Venom's lives.
They tested out their new found powers when they pushed Peter Parker onto a moving train. Peter survived, but everything went well in Venom's plan. He suceeded in making sure that the symbiote is able negate Spidey's Spider-Sense. Then, a few weeks later, Peter was clibing a building, and Venom grabbed his foot and Peter fell. Once again, Venom was succesful in making sure his spider sense was useless towards Spidey.
It was then time to strike full and center. With the knowledge of the symbiote, Venom decided to terrify Mary Jane by appearing in front of her and making her think it was Peter. She then told this story to Peter, and he immediately thought of the symbiote. Spidey tracked down Venom and the two fought a hellacious battle, until Spidey remembered that he can separate the symbiote with the help of a sonic gun. So Spidey went to FF Tower, got the gun and defeated Venom. The 'Lethal Protector' was sent to the Vault.
Despite escaping the Vault and paying frequent visits to Mary Jane, the Black Cat and even aunt May, Venom couldn't defeat Spider-Man. At one point, Brock was sent to prison and the symbiote was someplace else. In prison, Brock's cellmate was mass serial killer Cletus Kasady. Then when the symbiote found Brock, the spawn of the symbiote bonded with Kasady. They became 'Carnage'. Peter managed to make Venom believe that Peter himself was dead, so feeling that he had accomplished his goal, Venom 'retired'.
It wasn't until that Spider-Man discovered the existance of Carnage that he sought after Venom's help. Along with the Human Torch, Spider-Man got Venom's trust and the weird duo went off to face Carnage. They defeated Carnage but Spidey double-crossed Venom and they were both taken into captivity.
Months later, Spider-Man got Brock's ex-wife to convince Venom to stop killing and hurting people, it didn't work, but Venom left New York only if pidey promised never to interfere in his life again. But just several weeks later, the biggest killing spree in New York history took place. It was 'Maximum Carnage'. Carnage, Shriek, Carrion, Demogoblin and the Spidey doppelganger killed thousands of people. So Venom heard about this and returned to NY. With the help of Venom, Captain America, Firestar, Cloak & Dagger and others, Spidey managed to defeat the villains.
Venom would then wander around and he'd run into many adventures. Then one day, he'd meet the new hero, the Scarlet Spider. The new hero did something that Spidey had never done, soundly defeat Venom.
From there, more adventures would come his way. Then a special goverment agency "hires" Venom to kill J, Jonah Jameson, because JJJ has been snooping around on anti-mutant and Presidential candidate Greydon Creed and his friend, Bastion. When Venom is close to capturing him, Spidey makes the save. The hero fights Venom, until Spider-Man pulls a piece of concrete from the high-rise which falls then detonates smoldering dynamite behind Venom. Venom is knocked out; he has selected amnesia. The two are separated once more.
Venom goes to Carnage's cell at the Vault and 'absorbs' his 'son' in order to punish him for his deeds. He would later join the Sinister Six, along with Kraven II, Electro, Sandman, Vulture and Mysterio III in order to get revenge on Doctor Octopus. Venom would betray them and hunt them down one-by-one. He would even manage to almost fatally kill the Sandman.
A few months later, the symbiote finds its way towards an amnesiac Brock. With the two reuinted, Brock remembers his hatred towards Spider-Man, but he does not remember his identity. That is only fueled when his ex-wife Ann Weying commits suicide because she fears the symbiote too much.
Senator Ward manages to separate the symbiote and Brock for a long time. During this time, Brock believes that his 'soul' (the symbiote) has forever left him. The symbiote refuses to help a dying Brock, since it is pregnant and it wants Spidey's adrenaline in order to care for both of them. Spidey manages to save Brock's life by merging him with the symbiote once more. Now Venom is more lethal than ever, and wants revenge.