kingmaker
From Longman Dictionary of Contemporary Englishkingmakerking‧mak‧er /ˈkɪŋˌmeɪkə $ -ər/ noun [countable] CHOOSEsomeone who influences the choice of people for important jobs Her death thrust Newman into the position of kingmaker.From Longman Business Dictionarykingmakerking‧mak‧er /ˈkɪŋˌmeɪkə-ər/ noun [countable] journalism someone who influences the choice of person for an important job or positionHe will not run for office if he thinks he might lose; instead he will seek to be a kingmaker.