KINGMAKER
kingmaker
(noun) an important person who can bring leaders to power through the exercise of political influence; “the Earl of Warwick was the first kingmaker”
Warwick, Earl of Warwick, Richard Neville, Kingmaker
(noun) English statesman; during the War of the Roses he fought first for the house of York and secured the throne for Edward IV and then changed sides to fight for the house of Lancaster and secured the throne for Henry VI (1428-1471)
Source: WordNet® 3.1
Etymology
Noun
kingmaker (plural kingmakers)
Someone who has strong influence over the choice of a leader.
(game theory) A player who is unable to win but powerful enough to decide which of the other viable players will eventually win.
Usage notes
• Mostly used for people with powerful influence in choosing a candidate for public representation.
Source: Wiktionary