Colossal Titan

The Colossal Titan, as its name implies, is the largest and most powerful Titan glimpsed thus far in the series. It is the entity responsible for the destruction of Eren and Mikasa's home district, as well as marking a turning point in the war between humans and Titans. Up until its appearance, humanity had been relatively safe behind the massive walls they erected, but the Colossal Titan is able to break through these and allow its smaller brethren in. It is the closest thing to being a primary antagonist for the series.

Story
The Colossal Titan appears in Chapter 1 in the year 845, shortly after the history of the world and humanity's situation have been introduced, along with Mikasa, Eren and Armin. Its mere presence is enough to cause considerable panic amongst the population, as it is tall enough to see completely over the wall that is supposed to keep all Titans out. Within moments of its appearance, it attacks, repeatedly kicking the wall gates to the point that they rupture and open a hole large enough for other Titans to pass through. It then disappears after causing considerable structural damage to the wall, but does not attempt to participate in any meaningful way in the ensuing massacre itself.

It reappears five years later in 850, again breaking through the walls so that its brethren can once again devour the humans inside. It is immediately attacked by Eren Jaeger, however, it first repels and blinds him with vapour from its high temperature body before vanishing completely from view. It has thus far not made a reappearance.

Appearance
The Colossal Titan possesses a very distinctive appearance and a number of unusual features. First of all, it is roughly 60 metres tall, making it around four times the height of any other Titan seen thus far in the series. It also has an extremely high body temperature even compared to other Titans-it constantly produces smoke/steam vapour from its body in vast quantities, as well as being able to produce said vapour in sufficient quantities to blind and knock back soldiers in its immediate proximity. Just getting close to it exposes humans to an incredible, furnace like heat.

Abilities
As could be expected from its massive size, the Colossal Titan possesses an enormous level of strength, enough to rupture the gate sections of Wall Maria and Wall Rose with a single kick, as well as grind off the top level of Wall Rose with a swipe of its mighty arm. As noted by Eren when he begins his attack, the Colossal Titan also seems to possess a level of intelligance and tactical planning, in that it first attacked the top of Wall Rose to destroy the cannons placed there prior to vanishing and allowing other Titans to invade.

The Colossal Titan is one of the more hevaily deformed Titans seen in the series-it appears to lack skin entirely and its jaw and facial structure seem to be heavily altered from the human norm. Its feet are also quite different to those of a human and other Titans, as they are swollen and pillar-like in appearance, possibly to help support its incredible mass. Its physiology is modeled after the male gender, but like all Titans, it lacks obvious sexual organs.

Finally, it is highly likely that the Colossal Titan is one of those able to assume a human form at will, as evidenced by its vanishing act immediately after attacking the walls-it is likely, as discussed by the members of the Forward Squad later on, that the Titan shifted back to human form and escaped with the aid of 3D Manuever Gear immediately after destroying the gates on both occasions.