(n.) A member of the lobby; a person who solicits members of a legislature for the purpose of influencing legislation.

Rasputin Svengali VIP access bad influence big wheel court eminence grise five-percenter friend at court good influence gray eminence heavyweight hidden hand influence influence peddler influencer ingroup key kingmaker legislative lobby lobby lobbyer lords of creation man of influence manipulator open sesame parliamentary agent powers that be pressure group registered lobbyist sinister influence special interests special-interest group special-interest lobby the Establishment very important person wheeler-dealer wire-puller