Titan

Titans (also called Giants, Riesen and Colossi) are a species of hairless primates that walk on their hind legs, ranging in height from 3m-15m tall. Titans possess a natural instinct to attempt to devour human beings, in fact this seems to be the only species they prey upon. They do not appear to require oxygen, food or water to survive, though it has become apparent that they can tire after very long periods of time. It is generally agreed that they draw energy from the sun, with some stipulating that they may use a process similar to photosynthesis in plants.

Titans possess extraordinary regenerative abilities, and can heal from any injury within a matter of minutes. Only one injury has been found to be fatal: extensive damage to the nape of the neck. Titans' have a swelling of additional muscles in this area, and it appears to house some kind of complex nervous system. It is assumed that this system controls the regenerative process, since once it is destroyed the titan will die. This is often regarded as strange, since it is clear that titans possess a brain capable of driving their motor functions etc, but this does not appear to be required in order for the titan to survive, and cannot sustain life without the nape.

Titan Classifications
Titans are typically divided up based on their behavioural patterns. It is sometimes mistakenly thought that there is a steady linear increase in intelligence between each of the three classes, but this is by no means consistently the case. This pattern does appear in the majority of titans, but many Divergent class titans have exhibited extremely low intelligence, comparable to that of a Convergent class. Classification is thus based entirely on behaviour.

Convergent
By far the most common variety of titan, Convergent class titans are both simplistic and predictable in nature. A Convergent will wander placidly, seemingly at random, until it becomes aware of the presence of one or more humans. Due to a titan's keen olfactory senses, it will usually become aware of a human by smell first of all. Once aware of potential prey, the titan will pursue until either it devours the human in question or it escapes.This pursuit is not unconditional, as Convergent types have been known to withdraw after repeatedly experiencing significant bodily harm.

A Convergent will approach its prey slowly until it can establish line-of-sight to it. At this point it will either sprint towards the prey and attempt to seize it in its hands or jaws, or, if the victim is somehow not directly accessible, it will reposition itself at an urgent pace. Convergent class titans are not deterred by heights or intervening structures and will charge a human in such a position regardless. Once the prey is seized the Convergent will ingest it; whole if possible and in pieces if not.

Divergent
Significantly less common than Convergent class titans, Divergents are possessed of radically abnormal behavioural patterns. The actions of a Divergent are extremely difficult to predict, to the point that many think it impossible. They will on occasion demonstrate greater intelligence than Convergent class titans, attempting to move around artillery batteries and strong points or evading ambushes. Some eye witness accounts even seem to suggest that Divergents can play dead. The titan throws itself to the ground and by some unknown means causes its flesh to begin to dissolve, expelling steam. When humans approach, the titan becomes active again, attempting to seize and devour those nearby. All Divergent's show the same instinctive desire to hunt and devour humans as Convergents, though instances have been found where Divergents ignore specific humans in favour of others, regardless of proximity.

Coordinate
The rarest and by far most dangerous class of titan, a Coordinate is a titan possessed of full human-like intelligence. Currently, only three instances of this class have been confirmed to exist. These titans appear to be able to direct and control titans of other classes and have done so in order to bypass human military elements. All Coordinate class titans have to date had significant physical characteristics and abilities not found in other titans. These include the ability to scream at exceptionally high volumes, the excretion of an extremely hard crystalline substance as a means of protection and the growing of thick plates of bone that function as armour. Peculiarly, all three documented Coordinates possessed no skin, instead displaying exposed muscle, fat and sinew.

Though they are clearly intelligent, Coordinate class titans still ingest humans. Unlike other members of the species however, there does not seem to be an overpowering instinct compelling a Coordinate's actions. This means that, disturbingly, these titans make a conscious choice to kill and devour humans. Worse still, Coordinates have in the past shown the ability to understand human speech, though no instances of a Coordinate speaking have been documented. A Coordinate may make very clear signs of listening to a human speak, as well as some limited signs of comprehension, but all attempts at negotiation have failed.

Elements of personality have also been consistently observed. The so-called Diamond Titan displayed signs of curiosity towards humans on numerous occasions, choosing to observe from a distance without engaging. It was seen to examine an ammunition wagon, along with the shells scattered nearby. The Armoured Titan appeared to show sympathy for animal life, as several eye-witnesses claimed that it unhitched and released several panicked horses. In his memoirs Marshal Helmuth von Moltke claimed that the Howling Titan had deliberately sought him out, only to watch him retreat at a distance with "a posture that spoke undoubtedly of mockery and superiority."