Rebecca Chambers: is the main character of the Zero chapter. She's smart, resourceful and a shitty, shitty piano player. She's certainly the biggest anomaly of the entire Resident Evil series as she's eighteen and somehow is the First Aid Specialist on the STARS Bravo team. She's also an odd character because in Zero she's almost bad ass at some points and in the original and remake she's a coward and can't even take on a Hunter while in Zero she can take on a room of them. What makes her an even bigger question mark is the fact that she's skilled with a huge variety of weapons when she's as young as she is. She shouldn't have even graduated from the training necessary to become a First Aid Specialist, let alone weapon training.
Billy Coen: is the secondary main character of the Zero chapter. He's a former military man, who has apparrently killed a large number of people. Billy is the only character in all of the RE series that has a realistic skill set. He's in his mid 20s and an ex-military officer so it is very likely he could have mastered all the weaponry and skills necessary to take on the monsters of the T-Virus. As you can see by looking at Billy he's a very strong man and he's so far the only playable character in any Resident Evil game who is strong enough to literally throw a Hunter off of him when attacked by one. To go along with his superior strength he's also a walking tank. While Rebecca can take only a few hits before she's near death, Billy can take over five before he's even half dead. On Easy, Billy is capable of taking close to a dozen hits from a Hunter and is most definitely the character of choice for bosses.
Mysterious Man: some how controls the undead by singing. Could he be a T-Virus mutant, or is he something far more sinister? He's obviously in control of at least the Leeches that infest the facility and he also looks like a younger version of the former head of the facility, Dr Marcus. Could he be his son? Or even his Grandson?
Albert Wesker: is the commander of STARS. He obviously has ties to both Umbrella and the Raccoon PD, could this connection be a precursor of events to come? Or is Wesker's involvement with Umbrella purely in his own interested?
Dr. William Birkin: is a genius scientist and takes great pride in his work for Umbrella. Or so we'd like to think, whatever Wesker is planning it's obvious that he's in on it. Whether he's a pawn or not is up in the air. Birkin replaced Dr Marcus as Umbrella's top T-Virus researcher and has since moved on to a more advanced form of the T-Virus known as the G-Virus. Allegedly Wesker he has supplied Wesker with a sample of this enhanced virus...