A valuable employee, manager or subcontracted person who brings new business to a company. Bloomberg Financial Dictionary
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rainmaker rain‧mak‧er [ˈreɪnˌmeɪkə ǁ -ər] noun [countable] informal
someone who makes a lot of money for a company, for example by attracting rich clients:
• His law firm almost lost its key rainmaker to another firm.
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rainmaker UK US /ˈreɪnˌmeɪkər/ noun [C]
► someone who makes a lot of money for a company or who helps someone or something to succeed: »
The firm needed a rainmaker to bring in business and to raise capital.
»For the Democrats, he became a valued rainmaker, contributing nearly $1 million.
Financial and business terms. 2012.