Leon is a rookie cop on his first assignment for S.T.A.R.S. in Raccoon City. As in the original game, you will be able to control another character for a portion of the journey. The character that you get to control with Leon is a woman named Ada (Interesting Fact: Think back to the RE1 and the password to unlock one of the doors in the lab... That was Ada... Hmmm...). Contrary to what you may think, Ada, not Claire, is the woman who shoots at you in the S.T.A.R.S. room in the Police Station. Leon's quest is also supposedly going to be a little easier than with Claire. 
Leon is an idealistic rookie cop. He has quickly become disenchanted with the very system he is trained to uphold as he learns the harsh realities of the real world. He is somewhat reckless and brash, and certainly not as naive as his outward demeanor would have the casual observer believe. Leon is highly qualified for his job and his sense of humor makes him a very likable officer despite his rowdy attitude.

Claire is, as you can probably tell by the name, Chris' sister (Chris was in Resident Evil 1). She was a last minute change in the story line and replaced the "Elza Walker" character that everyone thought was going to be the girl in RE2. Claire's quest in RE2 will most likely turn out to be harder than Leon's. True to RE form, you will get to play as another character while on your journey as Claire. You get to control a little girl named Sherry. It looks like this girl will not be able to handle any weapons, unfortunately. 
Claire is a light-hearted and articulate modern woman. Her intelligence and optimism combine to make her both worldly and keenly aware of her surroundings. While Claire is a bit of a tomboy, she is very attractive and retains very feminine qualities. Her demeanor softens considerably when she deals with children. She can also be described as somewhat of a wild girl. Both extroverted and self-confident, she is typically the first person to try things many other would not. With her strong opinions on most issues, she can come across as quite sarcastic. 
 

Ada is a very professional woman, highly skilled and intelligent. However, she also can come across as very condescending with her tendency to talk down to those she deems "inferior" to herself. This is most evident in her tone of voice when addressing others. She is a Chinese-American who was engaged to be married in the near future. Her fiance was the scientist who wrote one of the letters in RE1.

In two different places, you will get to play as Ada instead of Leon. He get's into certain situations where you can't get out of without outside help, like Chris did with Rebecca in RE1.

Sherry a minor character in this game. She is the daughter of Annet Birkin who's husband worked for Umbrella and who made the G-virus. You will come upon her a few times throughout the game. She is probably lost in the police station when you find her.

Annet Birkin is the mother is Sherry Birkin. She is also the wife of Jon Birkin, the man who worked for Umbrella and who made the G-virus that made everyone into Zombies. You will come upon her by the entrance to the sewers where she will shot you (Leon) and then again a few times before the end when she kills Ada by throwing her of the side of the platform 100 meters up (cool demo).  

Ben is a very strange man. He claims that he knows what's going on in the town Raccoon City. The first time you meet him with Leon at least is in the prison cell (by the Kennel). You are there with Ada who you meet at the Parking lot. Ada has heard that Ben told the local newspaper that he knows what's going on. He tells you the whole story. Later Ben is eaten (from the inside) by a giant monster, a really cool scene.

This is a man that you meet the first time you are in the main hall of the Police Station (You will get to him by going through the far left hand side door in the main hall, right across from the computer). He will give you a key card to open all the doors in the main hall. Later in the game he has turned into a zombie and you have to kill him. 
 

This is the man that you stumble upon when you have entered the gun shop. He will have a short conversation with you before being eaten alive by 4 zombies who break the the glass to the gun shop. If you are playing with Claire he will be really sexist saying this like, "..babe", "..honey" etc.