Kingmaker

n. person who has great political power and is able to influence the selection of candidates for office

"Kingmaker" is a term originally applied to the activities of Richard Neville, 16th Earl of Warwick during the Wars of the Roses in England. The term has come to be applied more generally to a person or group that has great influence in a royal succession, without being a viable candidate. Kingmakers may use political, monetary, religious, and/or military means to interfere in the succession. Examples include:Warwick, the Kingmaker.Nogai Khan who influenced succession in the Golden Horde.
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Noun
1. an important person who can bring leaders to power through the exercise of political influence; "the Earl of Warwick was the first kingmaker"
(hypernym) important person, influential person, personage

The title of Richard Neville, a powerful English nobleman slain at the Battle of Barnet , 14 April 1471. Also a game by Avalon Hill, popular with re-enactors, dealing with the Wars of the Roses .

Synonyms and related words:
Machiavellian, Rasputin, Svengali, VIP, access, bad influence, behind-the-scenes operator, big wheel, court, eminence grise, finagler, five-percenter, friend at court, gamesman, good influence, gray eminence, heavyweight, hidden hand, influence, influence peddler, influencer, ingroup, key, lobby, lobbyist, logroller, lords of creation, machinator, man of influence, manipulator, open sesame, operator, pork-barrel politician, powers that be, pressure group, sinister influence, special interests, special-interest group, strategist, the Establishment, very important person, wheeler-dealer, wire-puller