In America a "chef" is anyone who cooks. In a kitchen the "chef" is someone you're payed to say "yes" to. Chef means "boss" in French. The chef is the boss. The chef de cuisine is the big boss. Some kitchens have an assistant boss (or bosses) called (a) sous chef(s). It's really that simple. In the kitchen, everyone else is a cook. If you ask a cook what he does, (s)he'll usually say, "I'm a chef, well I'm a cook." Friends and family always refer to their cook friends and relatives as "professional chefs." Always.
By usage the sentence, "He's a chef" is as meaningless as, "She's a gourmet cook."
Take a look at Chef - Wikipedia, the free encyclopedia
The descriptions of archaic station responsibilities in this article are as good as any and better than most. That being said, the kitchens described in this article probably don't exist outside of the very largest restaurants. Typically those are hotels or chains. Chain restaurant kitchens are only loosely organized around traditional brigade -- in that they're generally pushing some sort of theme food off on their customers and the kitchens are organized around the specific menu. Hotels with "fine dining" may be the last refuge of the true brigade.
In most modern kitchens the brigade roles are very blurred. There are also modern titles. For instance, the grill/roast station is called "turn and burn;" the saute station is called "hot pan," and most line cooks spend most of their time cooking hot pan; plating is usually done by the most senior chef in the kitchen at what's called "the hot plate;" some sauces are made to order at the saute station, but many (if not most) are made during prep by anyone or any number of people of various job descriptions -- and so forth.
The term "executive chef" always tickles me. Toque and a briefcase, I guess. Sous-chef might be the most elastic description of all. In some kitchens they're "men, equipment, time-cards and ordering" and almost never cook except to fill in for an absence or a rush. In other kitchens, the sous-chef handles more volume than anyone else.
The old brigade system worked best for kitchens with varied menus turning several hundreds of covers a night. That's seldom true of fine dining anymore; and most good kitchens are organized around the principle of whatever works best and cheapest.