The Koch political empire was built with Nazi money after their dad built an oil refinery for Hitler

The father of billionaires Charles and David Koch helped the Nazis build a major oil refinery, according to a new book about the rise of wealthy and influential conservative activists.

Author Jane Mayer describes in "Dark Money" how rich donors such as the Koch brothers, Richard Mellon Scaife and Harry and Lynde Bradley have steered modern conservatism through their considerable campaign contributions, reported the New York Times.

Fred Koch, whose sons wield great influence in the current Republican Party, made a fortune overseas in the years before World War II, the author writes.

The American Nazi sympathizer William Rhodes Davis hired the elder Koch to build the third-largest oil refinery in the Third Reich that served as "a critical industrial cog in Hitler’s war machine," the newspaper reported.

The oil refinery was approved by Adolph Hitler himself -- but that's not the only candidate for history's greatest monster with whom Fred Koch did business.

The elder Koch, a founding member of the anti-communist John Birch Society, also built 15 oil refineries in the Soviet Union during Josef Stalin's purges in the 1930s.

Fred Koch later came to despise the Soviet dictator and became "paranoid about communism," David Koch said.

A spokesman for Koch Industries, which was founded by Fred Koch and passed on to his sons, said company officials had not participated with the author and had not read the book.

Mayer, a staff writer for the New Yorker, said the Koch brothers created their vast and hugely influential political network to trick other business owners into helping them pay for their continuing efforts to fight environmental regulations and other laws that limit their profits.

She also reveals a sealed 1982 deposition that outlines how one of their brothers took part in a blackmail scheme by Charles and David Koch to force their fourth and eldest brother into surrendering his claim to the family business.

The brothers threatened to tell their father that David Koch, who has since described himself as a socially liberal supporter of same-sex marriage, was gay.