kingmaker:
(plural: ‘kingmakers‘; for the right pronunciation, please click here)

the kingmaker (L) & the king
a person who has great power, control and influence over a large group of people and uses his/her power to make another person of his/her own choice the king of a country or the leader of a political party or even the chief of an organisation (though the ‘king maker’ has the power to become the king him/her self, he/she does not like to take up the position for different reasons),

Mrs Sonia Gandhi, the kingmaker in Indian politics
A powerful politician becomes a kingmaker when he/she refuses the topmost position and instead nominates a much weaker candidate to the position and uses his/her keeps that candidate in the position but runs the political and financial affairs him/herself.
Some ‘kingmakers’ of the past include Richard Neville in England, (the term ‘kingmaker’ is believed to have originated from his nickname), and Nogei Khan in Russian-Mongol politics.
Some of the modern day ‘kingmakers’ in the present world politics are: Dick Norris in making Bill Clinton the president, USA; Sonia Gandhi in Indian politics; Kakuei Tanaka in Japanese politics; and Graham Richardson in Australian politics.
