The Walking Dead is an American post-apocalyptic horror television series for AMC based on the comic book series by Robert Kirkman, Tony Moore, and Charlie Adlard. The series features a large ensemble cast as survivors of a zombie apocalypse, trying to stay alive under near-constant threat of attacks from the mindless zombies, colloquially known as "walkers". However, with the fall of humanity, these survivors also face conflict from other living survivors who have formed groups and communities with their own sets of laws and morals, often leading to hostile conflict between the human communities. Andrew Lincoln played the series's lead character, Rick Grimes, until his departure during the ninth season. Other long-standing cast members have included Norman Reedus, Steven Yeun, Chandler Riggs, Melissa McBride, Lauren Cohan, and Danai Gurira.