power broker 
noun
A person who deliberately affects the distribution of political or economic power by exerting influence or by intrigue: its parliament and prime minister are fronts for the real power brokers, a coterie of elite bureaucrats one of the biggest power brokers in Hollywood...
- Needless to say, he is a real power broker on the international film scene.
- In stark contrast to its nature during the foundational period in the 1970s and early 1980s, the Commission in large measure both sets the Community agenda and acts as a power broker in the legislative process.
- The real winner, though, is also the power broker behind the merger.
Derivatives
power-broking
- But the 10 new members should not have to rely on charity, any more than the older members should be able to impose their will by power-broking.
- His last period as Prime Minister was marked by old-fashioned power-broking between the parties within his five-party coalition, instead of the application of cautious government reform begun by his predecessors during the 1980s.
- In Spain and her former American colonies, in Italy and in the Balkans, constitutional appearances barely concealed older forms of power-broking, factionalism, and conflict.