The Colossal Titan (超大型巨人 Chō ōgata Kyojin?) is the Titan form of Bertholdt Hoover and humanity's greatest threat. It first appeared five years ago during the fall of Wall Maria and returned five years later at Trost.
The Colossal Titan is a 60 m class, four times the height of all the tallest common Titans. The entirety of its body bears no layers of skin, exposing red muscle and white tendons and ligaments. Proportionally, the Colossal Titan possesses a very small head and small arms, whereas the legs are incredibly thick and trunk-like.
The Colossal Titan's height give it a great advantage over humanity's defenses, possessing the strength to break through the gates of the Walls in a single kick. Additionally, the Colossal Titan is seemingly able to control the amounts of steam emitted by its body, acting as an effective defense against human attackers. With this power, the Colossal Titan is also able to completely vanish into steam in a matter of seconds.
The Colossal Titan makes its first appearance outside Wall Maria, terrorizing the population of Shiganshina and kicking a hole in the southern gate. Soon afterwards, the Titan inexplicably disappears in a cloud of steam. Its actions allow the normal Titans wandering outside to enter Shiganshina, where they begin to feast on its many inhabitants, including Carla Jaeger.
The Colossal Titan reappears five years later in the year 850, breaching Wall Rose so that its brethren can once again devour the humans inside. It is almost immediately attacked by Eren Jaeger, but it first repels and blinds him with vapor from his high-temperature body before vanishing completely from view as it did five years before. This attack prompts the Garrison to enact the Colossal Titan contingency plan for Trost District.
When Reiner, in a moment of exhaustion and desperation, reveals himself to be the Armored Titan and exposes Bertholdt as the Colossal Titan, the two transform into their Titan forms and battle against the Scout Regiment. As Reiner's Armored Titan battles Eren's Titan, Bertholdt fights against the Scouts with a partially transformed Colossal Titan. When the soldiers are ready to land a killing blow, Bertholdt once more uses his steam emission control to keep them all at a distance, and their ODM gear is unable to reach him in the continuous gusts of wind. Bertholdt's Colossal remains in this state of emission for a short time until Reiner faces imminent defeat in his struggle against Eren and calls for help. Hearing Reiner's signal, Bertholdt falls to the ground below.