David Koch, billionaire conservative activist and philanthropist, has died. He was 79.

He and his brother, Charles, co-owned Koch Industries, a Nebraska-based energy and chemical company, since 1983. David stepped down from running the Koch organization last year due to declining health.

The Koch brothers helped to build a massive conservative network of donors for organizations that work to mobilize voters and sway elected officials in support of libertarian-leaning economic policies.