What is the origin of the idiom "every Tom, Dick, and Harry" and when to use it?

The idiom "every Tom, Dick, and Harry" is an idiom that has been used in English since at least the 17th century. It is a way of referring to random or ordinary individuals without specifying their actual names. Tom, Dick, and Harry are common given names, and the phrase suggests that it includes everyone, regardless of their identity. People often use this phrase to describe a situation where many people, often of little significance, are involved or to express a sense of generality.