Callisto

☠ Extremely skilled and merciless combatant
☠ Familiar with a varied array of weaponry
☠ Creative with her resources
☠ Manipulative both physically and emotionally
☠ Very high pain tolerance

☠ Canonly through midway season 2
☠ Had a family she loved very much before the outbreak began in her town. Really, she doesn't even seem like the same person.
☠ Her town was exterminated, essentially, by someone leading a small militia to try and do away with the infected before they became a real problem and burned the town to the ground, slaughtering everyone except Callisto. Kind of messed her up big time. Apocalypse doesn't help that much, but she'd probably be pissed regardless.
☠ More than the zombies, she wants revenge on someone who murdered her family.
☠ Was left to raise herself, refused to trust anyone. Learned to fight and use them instead. Sees the world in a very black and white spectrum, locked in her own hatred. Tends to blame others and the world for her problems.
☠ Never was able to develop real guilt or empathy towards others. If she needs something she'll take it and fuck the people who had it before.
☠ Increasingly unstable psyche. Appears just as willing to kill zombies as ordinary people if it suits her. Though she's never lost sight of her main motivation, she enjoys slaughter just as much as the bloodthirsty girl with a few knives.
☠ During an attempt to steal a superstitious item rumored (though not proven) to make one immune to the virus (which means it'd be easy for her to get her revenge if she didn't have to worry about those pesky zombies), she got herself locked in an old mineshaft for many weeks, having to live off rats and what rainwater would come through. She'd been unwittingly released.
☠ Now more mentally unstable than ever, she's taken to wandering her way to the east coast looking for some form of entertainment. She was bored down there, after all.