A cook is a person who prepares food for consumption.
A cook is sometimes referred to as a chef, although in the professional kitchen, the terms are not interchangeable.
The term "cook" within a restaurant kitchen usually refers to a person with little to no creative influence on a menu and little to no command over others within the kitchen, such as a line cook. These are usually all members of a restaurant kitchen that are underneath the sous chef in the brigade de cuisine. Other establishments may have a relatively constant menu, often only having people that can prepare food quickly and consistently, having little need for an executive chef or sous chef. The kitchens in these particular restaurants would thus be entirely run by cooks intimately acquainted with the menu. This example would not include the short order cook, however, since they are capable and willing to cook items that are not on the menu.
Professional cooks were used in Sardinia during the Nuragic Age, as proved by the typical sculptures of the Bronze Age, and in Mycenaean Greece and they are mentioned in Linear b syllabic script.   The first Olympic champion listed in the records was a cook, Coroebus of Elis, who won the sprint race in 776 BC. 
Lawrence of Rome, traditionally a patron saint of cooks and roasters, is reported to have said as he was being burned at the stake in the third century, "I'm roasted on this side. If you want me well done, it's time to turn me over."