Titans were a species of giant man-eating humanoids that served as the catalyst for the events in the Attack on Titan series. The people inside the Walls were taught that they first appeared 107 years prior to year 850 and rapidly exterminated humanity to the point of near-extinction. In reality, they were transformed humans known as Subjects of Ymir, and had existed for nearly 2,000 years. However, after Eren Jaeger's death and Ymir Fritz's decision to relinquish her power, all the Titans returned to their human forms, thereby rendering the species nonexistent.
Appearance: Titans greatly resembled nude human beings. They were bipedal creatures (with a few exceptions) with the same number and arrangement of limbs and features one would expect in human beings. ) to apparently lacking skin and subcutaneous tissues, although they did not bleed from such deformities and would regenerate the same deformities if injured, indicating that they perhaps possessed some other mechanism to compensate for this.
History: Around 2,000 years ago, a slave named Ymir discovered a large tree while fleeing from her masters, the Eldians. The tree had an entrance that led to a pit full of water. Unaware of the water, Ymir entered the tree and immediately fell into the pit.
Trivia: Despite their English name originating from the of , the Titans of Attack on Titan are much more influenced by the of . " Some Titans are modeled after friends and acquaintances of Hajime Isayama. Sometimes, he will even take requests.
Source: Titan (Anime), available under CC BY-SA 3.0.