In what is being called an "amicable" split, "Walking Dead" showrunner Glen Mazzara is leaving the show. Vulture is reporting that Mazarra and AMC are splitting up, but that he will stay with the show through end of the second half of season three. Mazzara took over as showrunner in the second season after the show's creator Frank Darabont left. It was also announced on Friday that the show has been picked up for a fourth season.