manipulator (n.)

• access
• agent
• calculator
• conductor
• court
• driver
• engineer
• functionary
• handler
• heavyweight
• influence
• ingroup
• intriguer
• key
• kingmaker
• lobby
• lobbyist
• machinator
• maneuverer
• operative
• operator
• pilot
• runner
• schemer
• steersman
• strategist
• tactician
• wire-puller