David Koch and his brother Charles Koch made their fortune with Koch Industries, a huge oil and gas conglomerate which is among the biggest private companies in North America.
David and his wife Julia met on a blind date and married in 1996.
Related: The Koch Brothers in 80 seconds
The Koch family is known for its strong political beliefs and philanthropic work.
The Koch brothers are considered some of the most powerful people in American politics because they donate a vast amount of money to support Republican candidates.
The family is also very involved in the arts. Julia is on the board of directors at the School of American Ballet.
