Literal or figurative source of great wealth, like a mine that yields gold. Can refer to a business, investment, or opportunity that generates large profits.
This new venture is truly a gold mine.
financial backer; patron; source of funds
A person or organization that provides money, like a sponsor or angel investor. Often used in contexts where someone is the main source of financial support.
rich person; moneybags
A wealthy individual, often with a nuance of being a source of money for others. Can be used somewhat colloquially or jokingly.
I hear that person is the richest in town.
He is the financial backer of our project.