"Big cheese" is an English idiom usually used when someone is making a reference to the boss of some organization. This phrase can also be used to describe anyone who is important in some aspect of life when compared to others. At times, someone using this phrase might be making snide reference to how the person being described is a bit pompous in the way he or she acts. People began using this phrase in the early 20th century, when the idiom "big cheese" evolved from the European practice if simply calling someone "the cheese."
When people decide to use certain words and phrases to spice up their speech with colloquialisms known to all members of the culture, they have many idioms from which they can choose. Idioms are short phrases that have accepted meanings that are far different from either the origins of the phrases or the literal meanings of the words contained within them. Many of these idioms are extremely colorful and expressive, giving life to otherwise mundane words. One idiom indicating a person of importance is "big cheese."
In a work setting, someone described in this manner is usually the boss. It could also be a manager of a large group of people within the framework of the overall organization. The phrase gives the indication that the person has a certain stature within the organization that is in excess of what the normal workers possess. As an example, someone might say, "He used to be just a lowly night-shift worker like the rest of us, but now he's the big cheese."
Describing someone in this manner doesn't always mean that the person in question is the boss. This idiomatic expression can also refer to someone who possesses significant clout and importance. The person may be a powerful and impactful member of a society, or he or she might rule over a smaller group of people like a family. In this context, a person might say. "I never thought I'd see the day when that kid who used to borrow money from us would be such a big cheese."
The phrase originated in the 19th century when people were simply called "the cheese" to denote their importance. In the early 20th century, the phrase evolved into the "big cheese," adding an extra bit of emphasis to the adage. It is still popularly used today, although the context and tone of the speaker decides whether the phrase is a glowing compliment or snide barb.