Kingmaker is a term that usually refers to a person or group that has significant influence over who comes to power, but who is unable to take power directly. In the context of elective monarchy, the term is sometimes used to describe a member of the electoral college (like a prince-elector or the Holy Roman Empire). The kingmaker concept is routinely applied to political entities in electoral systems to define a relatively weak group that can tip the balance of election by joining one of the stronger sides (for example, to the battleground or swing states of modern United States presidential elections).
