Titans (巨人 Kyojin, lit. "Giant(s)") are a race of giant man-eating humanoids that serve as catalysts for the events in the series. The people inside the Walls are taught that they first appeared 107 years prior to year 850 and had rapidly exterminated humanity to the point of near-extinction. In reality, they are transformed humans known as the Subjects of Ymir, and have existed for nearly 2,000 years.

Appearance:
Titans greatly resemble nude humans. They are typically bipedal with the limbs and features one would expect in humans; however, they are all deformed to some extent in body proportions (enlarged head, small limbs, etc.). Many Titans have exceptionally wide mouths with an array of square teeth. The vast majority of Titans have a masculine body shape, although all of them lack reproductive organs.

Behaviour:
Unlike other species, Titans do not mate, nor interact with organisms other than humans; their sole purpose in life is to seek out and devour humans. They do not derive any real sustenance from humans either, as many of them did not taste human flesh for a century after the Walls were raised, but it did not affect their activity nor decrease their numbers. One explanation for this is that they seek a human who possesses the power of the Titans, for if a Titan consumes a human with it, said Titan will become human again. Some Titans do not react to pain and all will move as long as there is sunlight. Titans do not possess a complete, functioning digestive tract; they merely have a stomach-like cavity that eventually fills up with what they swallow. After consuming a certain amount, they regurgitate the contents of the cavity before they continue eating more humans. Most Titans show no signs of intelligence and act like mindless beasts; easy to trick, distract, and deceive. The Nine Titans are the exception: They have human level intellect due to being piloted by a human. However, some Abnormals are also able to sustain some of their former intelligence.

Physiology:
The body of Titans appears to violate several known laws of science, spontaneously generating both energy and mass. Their bodies are incredibly light, allowing them to stand and walk despite their size. Their extremely high level of activity and body temperature indicates the need for a massive intake of energy to fuel them, yet they apparently never need to eat at all, though most Titans kill their victims by appearing to do so. They possess and use vocal organs, but they do not need to breathe for survival. Titans draw their primary source of energy from the sun, as they become inactive when deprived of sunlight. Titans possess incredible regenerative abilities. Although it varies from Titan to Titan, they can regenerate lost body parts from seconds to minutes, even severed heads (unless the nape is severed with the head). The only known sure-fire way to kill them is by slicing an area one meter long and 10 centimeters wide on their nape. This is the location of the central nervous system of the Titan; in Pure Titans, it is only a spine of the human that got absorbed, but in the Nine Titans, it is an entire human body. Without a functioning nervous system to control it, the Titan dies. After death, Titan corpses rapidly evaporate to skeletal remains, then to nothing at all.

Types:
  • Pure Titans (無垢の巨人 Muku no Kyojin): Ranging from 2 - 15 m in height, these Titans compose the vast majority of observed Titans. They all resemble humans but with varying levels of deformity. Their only common feature is their mindless nature. They mindlessly attack nearby humans, making them easy to deceive. However, they are still dangerous due to their size, physical strength, and sheer numbers. They are often used as weapons of war, by Eldia in the pastand Marley in the present.
  • Abnormal Titans (奇行種 Kikō-shu no Kyojin): Pure Titans that display abnormal behavior or intelligence are classed as Abnormal. Abnormals often ignore nearby humans and charge to more important locations where they can do more damage. The Colossus Titans found inside the Walls are unusually large, similar to the actual Colossus Titan, and have hardening abilities.
  • Nine Titans (九つの巨人 Kokonotsu no Kyojin): The Nine Titans are fragments of Ymir Fritz's soul. Humans who inherit them have the power of the Titans, which enables them to transform into their inherited Titan at will, gaining its special abilities while retaining their human body and intelligence. A human with the power of the Titans has access to advanced Titan abilities, such as focusing regeneration to specific parts of the body to increase the healing rate.
    Titans of this type: Armored Titan, Attack Titan, Beast Titan, Cart Titan, Colossus Titan, Female Titan, Founding Titan, Jaw Titan, War Hammer Titan.