WASHINGTON (AP) – 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. He joined Koch Industries in 1970 and serves on its board. He was chief executive officer of Koch Chemical Technology Group, a Koch subsidiary. Charles and David Koch, each with an estimated net worth of $31 billion, tied in fourth place in 2012 on Forbes 500 list of the nation’s richest men.