Since any walker-fied backstories will need to be imparted largely through visual means, there can’t be complicated storyline webs.
Or perhaps close-knit family members, like a husband and wife, or a mother and daughter.
Which isn’t to say each individual within the show’s undead hordes will be getting exhaustive backstories, since that wouldn’t be very feasible for anyone.
To use Maggie Grace’s words, the message should be simple enough to convey on a shirt sleeve.