Wulfareen! EDIT: You could find him loitering as Old Man Bogan, but after you recruit him his bloodlust increases until he becomes the Wulfareen. As Wulfereen he can randomly run off on his own and go berzerk on the zombies, but also features his regeneration ability allowing him to recover hp during missions and without meds in the car.
THE Rocketcat: Similar to a feral cat. Gives 25 fuel each night. If he dies, he will explode similar to Melty-chan.
Add HUNK from RE (http://residentevil.wikia.com/wiki/HUNK), the coolest of coolest zombie slayer. You can name him HANK or SEXY or SMEXY or something I can't think of any great skill ideas besides his sprite would look really cool (we need more commando/police/soldier/facemask outfits). How about weapons have a chance at doing double damage? I think that would be a fun skill. Kind of like a "critical" attack with guns or melee.
Ronin Hood A decent fighter who has some kind of non game breaking perk when facing bandits. If your supplies go over a certain level they start giving them away to the poor and needy.
A lovecraftian Karl Thuhlu with tentacles. If he reaches max strength he creates vortexes that suck zombies to their death. If not fed for X days he soul sucks strength from others but makes them happier. His tentacles can either dual wield (if possible?) or he simply grabs zombies and rips them in two. If he converts the people in the car to his abysmal faith and they kneel before him, they get some sort of boosts but also lose charisma and paranoid attitudes etc. Hail to the Cthulhu And he can pick eight noses at once.
Professor Zombie You ought to put a nice suit on him and give him a cool goatee He knows all about zombies and he'll tell you pointless trivia about zombies from time to time
School teacher -> Walter White -> Heisenberg "SAY MY NAME!!!" He can be a civilized person at the start. Then in the end become bandit.
How about someone based on Maxwell Smart (Braxwell Dart?). Could wear a suit and maybe use his shoe phone to increase the number of survivors encountered. When he dies he could say "Missed it by that much!" - the sheer volume of in game quotes he could use is staggering. Or Boston Dowers? His power could be to make everything shagadelic. Basically I guess a bumbling secret agent of some type.
I've written a few of these down but I'm not saying which ones. Update should come out late tonight/early this morning. MFi support (the beginnings of it) and the SECRET SURPRISE that Toucharcade already revealed haha.
Jake Adventurer that wields a hook and has a knack for finding items. Swift Quiet and Quick-moving character with high stamina that has low damage and inventory space.