Diane Hendricks, whose ABC Supply is based in Beloit, Wis. has given Walker more than $540,000 and an additional $1 million to the Wisconsin Republican Party. She became a lightning rod during the recall after Walker’s opponents found footage of them discussing his plans to crack down on organized labor with new laws like the one he just signed, often referred to as “right to work” legislation.

MADISON - Wisconsin Gov. Scott Walker is running for President, or at least making all the noises, and he's backed by a huge war chest filled by many well know national conservative billionaire donors like the Koch brothers. But who is his the biggest donor?

The answer, revealed by John McCormick and Julie Bykowicz in Bloomberg Politics, is Diane Hendricks of Beliot, the billionaire head of the largest U.S. wholesale roofing supply company.

Hendricks, whose ABC Supply is based in Beloit, Wis., is Walker’s biggest individual political benefactor. She’s given more than $540,000 to his two gubernatorial campaigns and to his successful effort to defeat a 2012 recall vote. She gave an additional $1 million to the Wisconsin Republican Party.

Hendricks became a lightning rod during the recall after Walker’s opponents found footage of them discussing his plans to crack down on organized labor with new laws limiting union-organizing power, such as the one he just signed, often referred to as “right to work” legislation. “Any chance we’ll ever get to be a completely red state—work on these unions and become a right to work?” Hendricks asked. Walker’s reply: “The first step is we’re going to deal with collective bargaining for all public-employee unions, because you use divide and conquer.”

Since the death of her husband and business partner, Ken, in 2007, Hendricks has plowed millions into conservative causes. According to the Center for Responsive Politics, a nonprofit in Washington that tracks political spending, she gave $1 million to the conservative Freedom Partners Action Fund super PAC in September, enough to make her one of its top eight donors. Freedom Partners is backed by the billionaire brothers Charles and David Koch, who discovered Walker in 2009, when he was the top elected official in Milwaukee County.

Ken Hendricks epitomized the version of the American dream that Walker extols. A high school dropout, he started a business when he was 21. ABC Supply, founded in 1982, has more than 450 branches in 45 states and annual sales of $4.6 billion, according to its website. The family also owns Hendricks Holding, which invests in real estate, insurance, construction, manufacturing, and other interests.