The Attack on Titan manga and anime series feature an extensive cast of fictional characters created by Hajime Isayama. The story is set in a world where humanity lives in cities surrounded by enormous walls; a defense against the Titans, gigantic humanoids that eat humans seemingly without reason. The story initially centers on Eren Yeager with his childhood friends Mikasa Ackerman and Armin Arlert, who join the military to fight the Titans after their home town is invaded and Eren's mother is eaten. They are part of the 104th Training Corps, whose graduates assume different positions in the Military, including the Garrison Regiment, the Survey Corps and the Military Police Brigade. It is later revealed that the area where the Walls are located is called Paradis (パラディ, Paradi) and that it is the last territory of Eldia (エルディア, Erudia). There are other empires outside the walls, namely Marley (マーレ, Māre), of which several of its key leaders have infiltrated Paradis as Titans.