kingmaker

One who has the political power to influence the selection of a candidate for high public office.

One who makes kings; one who raises a porson to a royal throne: a title applied specifically to Richard Nevil, Earl of Warwick (died 1471), who was the principal agent in making Edward IV. king in place of Henry VI., and afterward in dethroning Edward and restoring Henry.

Someone who helps making a leader a force to reckon with, without having any desire for the position themselves.

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)

an important person who can bring leaders to power through the exercise of political influence