What is Attack on Titan?

Attack on Titan is a manga and anime written by Hajime Isayama. The story follows a protagonist Eren Yeager who lives with his friends Armin and Mikasa within the three walls of humanity. Outside of these walls exist ferocious beings called Titans that eat humans. Eren watches his mother get consumed by Titans and vows revenge which kicks off the main story. The story has deep messages about war and genocide, and takes many unexpected turns.