Attack on Titan

Attack on Titan (Shingeki no Kyojin, literally "The Advancing Giants" in Japanese) is a highly popular manga and anime created by Hajime Isayama. It's primarily known for two things: The titular Titans, which are bulding-sized humanoid monsters that eat people, and a very high body count due to said Titans. The manga was first released in 2011; the anime premiered in 2013, and FUNimation released an English version in May 2014.

Basic Plot and Themes
Attack on Titan takes place in a dystopian Earth where the Titans have overrun the planet for at least a hundred years. The remains of humanity live in an enormous walled city whose walls are built specifically to keep the Titans out. (There are three walls; Wall Shina/Sina, Wall Maria, and Wall Rose.)

The plot kicks off in 845, when a much larger Titan than normal breaks through the perimeter