1. Little Girl Zombie (Season 1, Episode 1: 'Days Gone By')
Because you never forget your first. Having just left the hospital, Rick spots a tiny tot wearing an adorable pink nightgown clutching a teddy bear. "Little girl, little girl," he calls. The child wheels her head around to reveal half a jaw and a deathly pallor; she lurches towards him, intent on eating his brain. (It's a nice shout-out to that legendary Night of the Living Dead scene of an unfortunate family reunion.) No matter how many other walkers we'd meet on the group's travels over the next five seasons, there's something about the primal shock of seeing this initial zombie that still resonates. We have seen the horror to come, and they look just like our kids. And thus our Walking Dead waking nightmare begins.