The Walking Dead shows the comic book’s character Mercer on screen for the first time.Released yesterday (July 1), the new clip readies viewers for the return of the hit AMC zombie drama’s final season by hinting at big battles and introducing Mercer, the leader of the Commonwealth Military.Mercer, played by Avengers actor Michael James Shaw, heads up the heavily armoured community that look set to come to loggerheads with Maggie (Lauren Cohan), Daryl (Norman Reedus) and Negan (Jeffrey Dean