What is the origin of the idiom "big gun" and when to use it?

The origin of the idiom "big gun" can be traced back to the military context, where large and powerful guns were used as weapons of great force. The association between these powerful weapons and influential individuals or organizations may have led to the figurative use of "big gun" to describe those who possess significant power or influence. It is used to refer to a person or an organization that possesses great power, influence, or expertise in a particular field.