Bill

"...Portraying Bill as a once heroic army veteran, who though older and wiser, can still excel at physical combat."

- Ariel Diaz, Valve.

William "Bill" Overbeck is one of the four playable Survivors in Left 4 Dead, a Vietnam veteran who served in the US Army 1st Special Forces Group. His combat skills have helped to keep him alive, he is also the oldest of the group. In official media, he is usually seen wielding the assault rifle, probably to complement his back story. He and Francis have a strenuous relationship. He is voiced by Jim French. He often has a lit cigarette in his mouth.

Official description
It took two eventful tours in Vietnam, a handful of medals, a knee full of shrapnel, and an honorable discharge before the unthinkable happened: Bill ran out of wars. But now an army of infected has declared war on humanity. After decades of aimless drifting and dead-end jobs, Bill's finally gotten back the only thing he ever wanted: an enemy to fight.

Quotes and Captions
"See: Bill/Quotes and Captions"

Trivia

 * On the poster for Dead Air, his beret has a blue, star bordered U.S. Army General Service Beret flash on it, not the Yellow U.S. army 1st Special Forces Group beret flash as it appears in the game, and on the rest of the posters. It is also the only poster in which he isn't smoking his trademark cigarette.
 * Jim French, who voices Bill in Left 4 Dead, also voiced Father Grigori from Half-Life 2 and The Fisherman from Half-Life 2 Lost Coast.
 * Bill appears to have a rivalry, or just plain hatred of Francis, though the reason for this is unknown. It's possible that Bill and Francis knew each other prior to the outbreak giving them a friendly rivalry. Another cause could be Francis' hatred of the military (since Bill was once a soldier), or simply Francis' gruff personality rubs Bill the wrong way.
 * Bill is always seen smoking his trademark cigarette. Even when he is dead, it manages to stay in his mouth. However, when he dies, it is no longer lit, the only exception is during the opening scene where he doesn't light the cigarette until the end.
 * Bill fought in the Vietnam war. If the game occurs in 2009, that would make him at least 64 years old.
 * Bill is currently the only Survivor with a confirmed last name. "Overbeck" can be found on his military jacket.
 * If the player looks at Bill's back, there are scratches ripped in his jacket, exposing his shirt underneath. These are also visible in the trailer. It has been suggested that those scratch marks were made by a Witch. It is implied that Bill has experience in dealing with a Witch prior to meeting up with the other three Survivors. This theory is further reinforced when Bill tells Zoey, "Lights, off!" when the flash of lightening reveals the Witch's outline in the game's opening cinematic.
 * It is possible that Bill has Arthritis, considering his hatred of stairs, and his age. However, it is more likely that the knee injury mentioned in his official description hurts him when he walks or runs, so stairs would be even more painful. Either way, it has no significant impact on Bill's movements in-game.