David Koch, one of the wealthiest men on the planet and an influential libertarian political force, has died at age 79. Along with his brother Charles, the Koch brothers expanded their father’s empire into a global behemoth. Together, Charles and David are worth around $120 billion. Politically, they helped found the Tea Party movement, and pushed for so-called dark money to enter politics without restrictions. They have vast lobbying operations and Koch-funded think tanks at universities.