Titans

Titans (巨人 Kyojin?, lit. "Giant(s)") are a race of giant, man-eating humanoids that serve as the catalyst for the events in the 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 have transformed humans known as Subjects of Ymir and have existed for nearly 2,000 years.