The Survivors

The Survivors are people in the world who have not yet been infected, however the term is commonly used to refer to the four playable uninfected humans.

Playable Survivors
Each playable survivor has his or her own unique appearance, personality and backstory, making them easier to identify at a distance. Players can choose which Survivor they control in the lobby, or be automatically assigned to a Survivor that is not being controlled by a player when they join a game that is already in progress.

Non-playable Survivors
As well as the four playable survivors there are also known to be many more. Most remain unseen and unnamed however they are evident by graffiti left around most of the chapters, mainly in the safehouses.

Evacuation Personnel
During the finale of each scenario, a survivor in a vehicle must arrive to rescue the four main characters from their evacuation point. These survivors are never seen, as they are usually concealed behind the windshields of their vehicles, excluding the helicopter pilot from the No Mercy campaign. These survivors include the aforementioned helicopter pilot from No Mercy, the boat drivers (John and Amanda Slater) from Death Toll, the plane pilot from Dead Air, and the APC driver from Blood Harvest. In all cases you communicate with them via radio.

"churchguy"
A man whose voice clips were found in the demo's files. He appears to be afraid of infection, locking himself in the safe room that the Survivors must get through. It is later revealed that he was bitten by his friend, who became an Infected, and deemed himself immune to the virus after waiting an hour. Ultimately, he also becomes an Infected. His paranoia of the Infected drove him to insanity. He often says "better safe than sorry" and causes a mini-finale where he rings the church bell to attract a horde to kill the Survivors. His voice actor, Nathan Vetterlein, also voiced the Scout from Valve's Team Fortress 2.