The Symbiotes are a villainous race of parasitic alien beings featured in the Marvel Comics. They are goo-like creatures that attach themselves to a living host and feed off the negative emotions; furthermore constantly enhancing those negative emotions. This race consists of about 18 members.
If kept for too long, Symbiotes ultimately devour their hosts. In the film Venom (2018), it is revealed that Symbiotes, once merged with their hosts, devour said hosts' internal organs and consume them from inside out, killing them in the long run. This can be avoided if the symbiote feeds enough certain chemical (most likely phenethylamine) which found in either the human brain or chocolate to keep itself and the host stable and healthy.
Although began as benevolent species which believed in helping others, which they attempted to do by creating heroes through the process of bonding to the morally and physically ideal, hosts afflicted with chemical imbalances, emotional negativity (hate, greed, pride, stress, etc.) or cultural malignancy could corrupt Symbiotes, turning them into destructive parasites. Over time, corrupted Symbiotes became more widespread than their benevolent counterparts, establishing a space-faring culture dedicated to infecting and overtaking planets.
Everything comes detached from Knull (a being who was since the existence was only darkness), in a flash appeared the Celestials, Knull feeling that his kingdom of darkness was disturbed, decided to create a weapon to defeat the Celestials. This weapon would become the first of its kind known as All-Black.
The peoples cried out for mercy and their plegiaries were heard by a god, Thor, who with their rays managed to bring light to the Symbiotes who saw what Knull was able to do, so they dragged him to a planet to finally imprison him, surrounding him, leaving these Symbiotes behind. thousands of years, this race would be called Klyntar (although Klyntar in their language means cage). Venom belongs to this race, these beings in their majority had appeased their violence, but some of these beings became insasiblaes by controlling others and exploiting themt so that these clindar would be imprisoned, this prison would be broken and these clinchers would escpaparian and evetualemete one of them would meet with espiderman in Marvel's Secret Wars comic line, in which the alien suit bonded to Spider-Man, granting him greater power. After a while, Spider-Man learned that the suit was alive and taking over his life, so he had it removed a few times, as it kept coming back to him.
Eventually, the symbiote found another host: frustrated, angry newspaper reporter Eddie Brock. The symbiote bonded with him, and together they became the super-villain known as Venom, who had the same powers as Spider-Man, but stronger. Because the symbiote and Spider-Man were allies for so long, Spider-Man spider sense never registers Venom as a threat, making him even more dangerous. The symbiote-infected human always referred to themselves in the plural first person, saying "We" instead of "I".
Once, when Brock was separated from the symbiote and sent to prison, it returned and broke him free, making them Venom again. Brock inmate, the psychotic serial killer Cletus Kasady, involuntarily bonded with some of the symbiote's spawn, and they became one of Spider-Man's most dangerous foes ever: Carnage. Carnage was even more powerful than Spider-Man and Venom put together, showing that the symbiote sapped power from each host and gave it to its offspring.
The symbiote's two main weaknesses are sound vibrations and extreme heat. Other characters in the Marvel universe have become infected with the symbiote as well, including Deadpool, Scorpion, and Wolverine.
It has recently been revealed that the Venom Symbiote was, in fact, a deceased member of a race known as the Klyntar. After returning to its homeworld during his time with the Guardians of the Galaxy, part of a 'hero exchange program' while serving with the Avengers, Eugene "Flash" Thompson has now had the symbiote 'cured', unlocking new abilities and knowledge.