Zombies

I just overheard an aphorism I've never heard before, "every zombie needs a back story." I wonder if that's true. Well, certainly every zombie seemingly does have a back story. But do they need one? Not if they are just an extra in a movie or a statistic in some department of homeland security report.
Now, if the zombies win then I can't say whether pre-zomie lives will be important or not. I don't know what zombies value or how they see the world. All I know is they eat brains. If they win, what do they eat when the brains run out?