WASHINGTON (AP) -- They are the outsized force in modern American politics, the best-known brand of the big money era, yet still something of a mystery to those who cash their checks.
They're demonized by Democrats, who lack a liberal equal to counter their weight, and not entirely understood by Republicans, who benefit from their seemingly limitless donations.
These are the Koch brothers, and perhaps the first thing you need to know is that there are four of them.
The constant shorthand reference -- "Koch brothers," pronounced like the cola -- that lumps them all together shortchanges the remarkable story of four very different people who rode the Koch genes and the Koch money in vastly different directions.
Charles is the steady, driven one. He's grounded in the Kansas soil of their birth.
David is his outgoing younger brother. He's a New Yorker now, and pronounces himself forever changed by a near-death experience.
William is David's free-spirited twin, a self-described contrarian whose pursuits beyond business include sailing, collecting things and suing people (his brothers included).
And then there's the oldest, Frederick, who's as likely to turn up in Monte Carlo as at his apartment on New York's Fifth Avenue and doesn't have much to do with the rest of the lot.
They're all fabulously wealthy, all donate lavishly to charity, all tall -- Frederick is the shortest at 6-foot-2 -- and all are prostate cancer survivors.
Two of them, Charles and David, have defined the public notion what it means to be a "Koch brother."
In the eyes of the political establishment, it's the willingness to freely spend their awesome wealth in the pursuit of a smaller, more limited government. Among the executive set, it's their success at turning Koch Industries into a corporate behemoth whose reach extends into every corner of American life -- toilet paper to jet fuel, fertilizer to cattle.
Among Democrats? Well, it's the idea that success at business allowed them to advance a political agenda that is designed to benefit those businesses.
The other two brothers -- known in the family as Bill and Freddie -- cut their ties to the family business decades ago and don't show the same passion as Charles and David to change the world. One of them, if you can believe it, has even given money to Hillary Rodham Clinton. (That would be Bill.)
As Bill sizes up his siblings during an interview with The Associated Press: "David and I like off-color jokes, Freddie likes more sophisticated jokes." Charles? "Charles likes golf."
Let's start with Charles and David, the two in sync on business and politics who most people think of when referring to the "Koch brothers." To even pair these two together risks missing their differences, of both geography and style.
Charles is the white-haired alpha male at the helm of Koch Industries. Midwestern through and through, the 78-year-old still walks up four flights of stairs to work at Koch headquarters in Wichita, Kansas, each morning and eats his lunch in the company cafeteria.
After building Koch Industries into the nation's second-largest private company, he turned his business philosophy into a book, "The Science of Success," drawing on -- take a breath here -- "economics, ethics, social philosophy, psychology, sociology, biology, anthropology, management, epistemology and the philosophy of science."
"He's the most focused person I've ever met in my life," says Koch Industries general counsel Mark Holden, who's worked at the company since 1995. "A purpose-driven life, that's Charles. It's always, 'What's next? Let's focus. Let's keep moving.'"
What's next has become the next election. After spending decades promoting his libertarian ideas through think tanks and other educational organizations, some of which he founded, Charles wrote in The Wall Street Journal this spring that in the past decade he's seen "the need to also engage in the political process."
Thanks to changes in the nation's campaign finance laws, it's not possible to know for sure how much he and David have spent to create a sprawling network of groups working to promote free-market views, eliminate government regulations, fight President Barack Obama's health care law, oppose an increase in the minimum wage, shift control of the Senate to Republicans and oust Democratic officeholders -- from Obama to folks at the local level.
Money from Charles and David got Americans for Prosperity started, empowering the tea party activists who have tugged Republicans to the right. Eyeing younger voters, they back Generation Opportunity. Older voters? The 60 Plus Association, a conservative alternative to AARP. Their political hub, Freedom Partners Chamber of Commerce, has funneled cash to a Who's Who of conservative groups, including Concerned Veterans for America, the Republican Jewish Coalition and the National Rifle Association.