Definition of "kingmaker"

Alain, who is proud of choosing the extreme right but still didn't want his real name printed, is one of the 6.4 million [Marine] Le Pen voters who are now the kingmakers in deciding who becomes the next president of France. If the Socialist François Hollande topped the poll, beating the rightwing president, Nicolas Sarkozy, and gaining momentum for returning the left to the presidency for the first time in a generation, it is Le Pen whose high showing and third place now holds the election in the balance.

2012 April 23, Angelique Chrisafis, “French election: Marine Le Pen voters grapple with their role as kingmakers”, in Alan Rusbridger, editor, The Guardian‎, London: Guardian News & Media, archived from the original on 26 January 2021

However, a National-Act coalition would only have a slim majority, meaning Mr Luxon may need to secure the support of NZ First, whose leader Winston Peters has been kingmaker in previous Labour and National-led coalitions.

2023 October 14, Antoinette Radford & Graeme Baker, “New Zealand election: National party's Chris Luxon claims victory”, in BBC