Billionaire David Koch is stepping away from Koch Industries and the the Koch political network due to his poor health, leaving his brother, Charles, at the helm.

Why it matters: The Koch network has received considerable attention for its role in the rise of what the left calls “dark money,” with their donations funding substantial portions of conservative activism. The Koch brothers have also played a major philanthropic role in the U.S., and the David H. Koch Foundation alone has pledged or contributed more than $1.3 billion to cancer research, medical centers, educational institutions, and arts and cultural institutions.