Read more about Venom at: Wikipedia
Official Site: Marvel Comics
Venom, or the Venom Symbiote, is a Symbiote, an extraterrestrial life form in the Marvel Comics universe. The creature is a sentient alien with a gooey, almost liquid-like form. It requires a host, usually human, to bond around for its survival. In return the Venom creature gives its host enhanced powers. In effect, when the Venom Symbiote bonds with a human to form a supervillain, that new dual-life form itself is also often called Venom. Its second host Eddie Brock, after bonding with the Symbiote to become the first Venom, is one of Spider-Man's archenemies. Spider-Man was the first host it merged with before its evil motives were clear. After Spider-Man rejected it, the Symbiote went on to merge with other hosts and so began its reign as the villain known as Venom. Comics journalist and historian Mike Conroy writes of the character: "What started out as a replacement costume for Spider-Man turned into one of the Marvel web-slinger's greatest nightmares."
Venom has become one of Spider-Man's most enduring and popular foes. Indeed, he has become so popular that he is seen as Spider-Man's arch-nemesis, in terms of his popularity. Venom was ranked as the 22nd Greatest Comic Book Villain of All Time in IGN's list of the top 100 comic villains, 33rd on Empire's 50 Greatest Comic Book Characters, and was ranked as the 98th Greatest Comic Book Character Ever in Wizard magazine's 200 Greatest Comic Book Characters of all Time list.
Spider-Man first encountered the Venom Symbiote in Secret Wars #8, in which he unwittingly merged with it. After Spider-Man rejected it, the Symbiote merged with Eddie Brock, its most well-known host, in The Amazing Spider-Man #298 (May 1988). Its next host became Mac Gargan, the villain formerly known as Scorpion.
Originally, the Symbiote was portrayed as a mute and lonely creature craving the company of a host. More recently, it has been shown as increasingly abusive of its hosts, and having the power of speech. The Venom Symbiote has no known name, as "Venom" is essentially the moniker it has adopted since its history with Spider-Man on Earth. According to S.H.I.E.L.D., it is considered one of the greatest threats to humanity, alongside Magneto, Doctor Doom, and Red Skull.