The Gettys – $5B
The Getty clan earned most of the family fortune during the twentieth century thanks to the petroleum industry. The founders are none other than George Franklin and his child, Jean Paul. Originally from Ireland, the father-and-son duo had Irish and Scottish lineage. They traced their roots to Cullavmor, which eventually became what we now know as County Londonderry. George Franklin was a lawyer before he became an oilman. After making it big, he gave the proceeds of the company to his sons and told them to go into oil and gas. They followed his sound advice, and it worked out for the best. In 1916, they started Getty Oil. The mighty oil business is still under the control of the family, and the net worth keeps going up with each generation.

The Gettys – $5B