WASHINGTON – Billionaire David Koch has died at age 79. Koch was a major donor to conservative causes and educational groups. His older brother, Charles, said on Friday, "It is with a heavy heart that I now must inform you of David's death." The Kochs were best known for a vast political network they built that became popularly known as the "Kochtopus" for its far-reaching tentacles in support of conservative causes. The brothers founded the anti-tax, small government group Americans for Prosperity. David Koch was an engineer trained at MIT.