Drew Sharp (Season 5, Episode 5: "Dead Freight")
I know what you're thinking: Who? We never get to know, not really, and that's part of the tragedy. Drew Sharp is the name of the dirtbike-riding little boy who stumbles across Walt, Jesse, Mike and Todd's great train robbery in the desert, and pays for it with his life. Slapped on to the end of an exhilarating heist, his death was devastating – an indication of the kind of man Walt's new hire Todd really is, the final straw for Jesse (whose genuine love for children holds true now just as it did when he saw a kid orphaned by an ATM), and the moment at which Walt's ends-justify-the-means/what's-done-is-done platitudes are revealed for the monstrous excuses they really are.