What is the origin of the idiom "one's opposite number" and when to use it?

The idiom "one's opposite number" originated from the context of diplomatic, military, or business interactions. It refers to a person who holds a corresponding or equivalent position on the other side of a negotiation, discussion, or conflict. This idiom is primarily used to suggest a sense of symmetry or mirroring, as each person acts as a counterpart or counterpart to the other, representing similar roles or responsibilities in their respective organizations or groups.