Harry Osborn, Peter's best friend, was bonded to a mysterious symbiote in a desperate bid by his father Norman Osborn to save him from a terminal medical condition.
Because of the symbiote's influence on his personality, Peter refused to return the symbiote to Harry, even to save his best friend's life. Incensed, Harry extracted the symbiote from Peter and rebonds with it, transforming into Venom and wreaking havoc across New York City as Peter and Miles scrambled to stop him.
Harry Osborn is the primary host of the symbiote before giving it to Peter Parker, resulting in the iconic black and white symbiote suit and causing Peter's behavior to become more aggressive and dangerous. It's ultimately returned to Harry, however, who fully succumbs to its influence and becomes Venom.
After Harry encountered a sample of the Venom symbiote, he becomes its first host and uses it to become a superhero to impress his father, being referred to as the "Black Suit Spider-Man" by the media. Eventually, Harry succumbs to its influence and becomes "Venom" before being saved by Spider-Man.
Peter can't simply get rid of it. It's attached to him on the cellular level. The anti venom suit isn't alive per se. Like he doesn't have a voice or alien kind of host.
Marvel's Spider-Man 2 Peter's Lowenthal Gains His 19 Inches Symbiote Suit Back To Clap MJ's Scream
Why did Venom choose Eddie?
Venom came to empathize with Eddie's status as a "loser", eventually deciding to turn on its own kind and save the Earth from being invaded. The symbiote ultimately agreed to work alongside Eddie as a vigilante, to only hurt bad people despite its own confusion of how it can tell the difference of who is good or bad.
After a failed attempt at obtaining some of Spider-Man's blood to try and cure himself, Harry took a serum made by Oscorp. Instead of it curing him, the serum simply quickened the process transformed his entire skin, possibly also sending him insane.
The symbiote re-bonds to Harry, who is resentful that Peter initially kept the symbiote to himself due to its malevolent influence on him. Upon re-bonding with Harry, the symbiote transforms Harry into the monstrous Venom, who then kills Kraven the Hunter and creates symbiote nests around the city.
No, Harry Osborn has never been Venom in the comics.
After the symbiote was destroyed, Harry took a piece of the suit and was crowned the "Black Suit Spider-Man", and became a favourite of New York denizens as he took ample opportunity to humiliate Peter Parker.
To fix the damage done, he put on a performance-enhancing EXO-suit and stole a glider. Ultimately, Harry never cured himself, but the venom turned his disease into a weapon.
Having bonded with the symbiote, the two became the being known as Venom. During this time, it spawned seven offspring and a clone; its first child later had three of its own, producing the symbiotes known as Carnage, Scream, Lasher, Phage, Agony, and Riot.
However, becoming immortal from gathering the three is a misconception, as being a true Master of Death is realising and accepting the fact that everyone will die and there are worse things than death. Harry Potter collected the three Hallows and was willing to accept death and so became the Master of Death.
When a symbiote offspring of Eddie Brock, AKA Venom, merges with serial killer Cletus Kasady, the result is the nightmarish murdering menace known as Carnage!
Eventually, after Peter is fatally stabbed by Kraven, the symbiote transfers to him, manifesting as the Black Suit and healing him. Its powers enable Peter to fight off Kraven's Hunters, but when Harry requests the symbiote back, it refuses to return, remaining attached to Peter.
The symbiote genuinely wants to help Peter and believes that it's their responsibility to protect the innocent. Even if it means instilling fear and killing any villains that step out of line. After being separated from Peter, the symbiote was left angry at Mr. Fantastic for interrupting its bond with Peter.
Marvel Comics' new version of Venom has become the most powerful symbiote ever. Dylan Brock, the son of the original Venom host, Eddie, has unlocked a new power that allows him to sever a symbiote's connection to the hive mind, which makes him a threat even for the all-powerful Kings in Black.
Harry discovers that his father developed an advanced version of the Goblin Formula, but was unable to test it before his final battle with Spider-Man. After testing it, he ingests the new formula. When he spies Spider-Man investigating his townhouse, Harry loses his temper and attacks him as the Green Goblin.
After three days the Goblin attacked the limousine that Harry Osborn was in. Harry was shocked to know that the Green Goblin was his father and tried to keep Spider-Man and his team from hurting him, and every time they did it was clear that the Venom Symbiote was re-surfacing.
In the comics, Anne Weying was bonded with Venom, which led her into becoming She-Venom. She was also married to Eddie Brock, unlike the the movies, where she was engaged with him before breaking up later on.
Venom's symbiote has explained on many occasions that the Klyntar planet is practically devoid of emotions, yet over time he knows that he forms genuine love for Eddie. Venom bonds more with Eddie and experiences guilt, jealousy, and sadness over his other half.
Ultimately, Venom is the result of Harry's inner bitter feelings being unsuppressed, as well the symbiote's strong desire to be with its host. Due to this, Venom acts in a manner that suggests he is and has always been Harry, using both his memories and his motives to convert them as his own.
In the Spider-Man (2002) game, Harry Goblin is playable as the Green Goblin (Norman Goblin's original suit), making him the only Goblin to become both Goblins but the game isn't canon since Harry didn't discover his father was the Green Goblin until the end of the second movie.
Meanwhile, Harry finds love with Liz Allan and marries her, and they have a son Normie, named after his father. Though his descent into madness after taking the Goblin formula lands him in a superhuman prison. Liz couldn't testify against Harry so he was released from captivity.
