A fundraiser is a person who seeks out donations to a cause, campaign, charity, or some other venture. If you're a museum fundraiser, your job is to raise money to benefit the museum.
A fundraiser is a volunteer or a paid employee whose job involves soliciting potential donors — people who might be convinced to give money to a charity or organization. A fundraiser, in fact, might organize a fundraiser, a party that encourages financial support for a cause. Your ticket to a hospital fundraiser, for example, might cost $100, with most of that money going directly to the hospital's charity.