Final answer:
The term that defines an individual who works within an existing organization to exploit opportunities using personal resources is "intrapreneur."
Step-by-step explanation:
An individual or individuals who work(s) within an existing organization, using personal resources to exploit an opportunity, defines a(n) intrapreneur. Unlike an entrepreneur who establishes a new company, an intrapreneur is someone who operates within the confines of an existing company, bringing innovation and driving new business initiatives while using resources provided by the employer. This person is distinct from an angel investor, who provides capital for a business start-up in exchange for ownership equity, and is also different from a stockholder, who simply owns shares of stock in a firm.