The Klyntar - more commonly referred to as Symbiotes - are an extraterrestrial race from the Marvel Comics universe. These amorphous, symbiotic life-forms originate from somewhere in the Andromeda Galaxy and were believed to be benevolent, existing in a hive mind and capable of sensing the "voice" of the Cosmos. They endeavored to create an intergalactic peacekeeping society by using the symbiosis they need to subsist in order to transform worthy hosts into the ultimate noble warriors, the Agents of the Cosmos. However, to achieve this perfect symbiosis, the host must have a perfect blend of moral and physical ideals. If not, the resulting symbiosis would corrupt both the Klyntar and its host. Symbiotes are fully aware and sentient creatures, but when corrupted are also vicious and wild, compelling their hosts to violence and corrupting them.
Corrupt Symbiotes have become much more widespread across the universe than their benevolent counterparts over time and have used deceit and misinformation to convince most other races to fear and hate all Klyntar. This spread of universal distrust works to the advantage of the corrupt Klyntar in that it ensures a large variety of ideal hosts to bond with, making it all the easier for them to propagate and spread across the universe.
A Symbiote in its natural state appears to be little more than an amorphous blob of goo, though corrupt Symbiotes have also been known to sport features such as large white eyes and mouths filled with many sharp fangs. Symbiotes are capable of surviving on their own, though they become far more enabled when they bond with a host organism. They are capable of bonding with most life-forms, though generally prefer sentient, intelligent hosts (eg. humans).
Beings that bond with a Symbiote have all of their natural abilities heightened and gain new powers based on the biology of the Symbiote. All Symbiotes possess genetic memory, their knowledge and experiences ingrained into their very being, and they can share this memory with every new host they bond with. This also includes certain unique powers and abilities from previous hosts which become a permanent part of the Symbiote if it had spent a long time bonded to whichever host originally possessed that power.
Symbiotes also have significant effects on their hosts' minds. While the benevolent Symbiotes join with their hosts' minds harmoniously, the corrupt Symbiotes will generally force their hosts into accepting them, albeit with subtlety. This process is eased greatly if the host is already of a negative disposition, such as when the Venom Symbiote joined with Eddie Brock; both Brock and the Symbiote were already extremely embittered and resentful towards Spider-Man whom had severed himself from the Symbiote and who Brock blamed for the loss of his credibility. As the corrupt Symbiote and its host spend more time joined, the host becomes increasingly dependent on the Symbiote, becoming addicted to the power it offers. Corrupt Symbiotes also bring about negative emotions within their hosts which the Symbiote, in turn, feeds on.
Symbiotes are known to possess a number of weaknesses. They are particularly vulnerable to fire and sonic waves can cause them immense pain. Other more specific methods of weakening a Symbiote also exist, such as chemical compounds specifically designed to attack Klyntar biology.