A dozen potential Republican presidential candidates are about to sit down, one by one, with the biggest GOP donor in Iowa — a multimillionaire few people outside the state have ever heard of.

Bruce Rastetter, an agribusiness mogul who’s made a fortune in pork, ethanol and farm real estate, has long worked behind the scenes to help bankroll conservatives across the country, but Saturday is a public coming out party of sorts for Rastetter as he hosts the first-ever Iowa Agriculture Summit. It’s an event designed to promote farm policy in a state where pigs outnumber voters 10 to one, but it’s also a bold display of the political power Rastetter has amassed — and a reminder to candidates that his endorsement would be a big get ahead of the Iowa caucuses.

It’s an unusually public gig for a donor: Rastetter will chat with each candidate on-stage for 20 minutes before 1,000 Iowans and dozens of media outlets. He’ll get to ask Jeb Bush what exactly he thinks about ethanol, pepper Scott Walker with questions about EPA regulations and quiz Marco Rubio about where he stands on GMO labeling, if he wants. Chris Christie, Ted Cruz, Rick Santorum, Donald Trump and Mike Huckabee will enter the agriculture policy ring, too.

How the 58-year-old self-made millionaire assembled one of the biggest GOP cattle calls yet is illustrative of the influential network he’s built over the past several years, as he’s emerged as the state’s top Republican donor at both the federal and state level, donating nearly half a million and $1.1 million, respectively, since 2003, according to campaign finance disclosures — sums that are likely a fraction of his total giving to groups that don’t have to disclose their donors.

If you ask political observers in Iowa about Rastetter, the term “kingmaker” inevitably comes up, but Rastetter and his allies dispute the idea.

“I think I try to make a difference with what I do and what candidates I support, but I would consider myself more [an influencer] than a kingmaker,” Rastetter said. “Clearly not everyone I have backed has won.”

But Rastetter’s moves over the past decade look like a “how to” guide for becoming a political power player, with far more influence than other wannabe Iowa kingmakers. He started by building agribusiness empires in some of Iowa’s key sectors— including pork and ethanol — then built close relationships with Iowa’s political elite, like Gov. Terry Branstad. He slowly upped his contributions to Republican causes beyond the state in 2008, giving tens of thousands to Karl Rove’s American Crossroads and the National Republican Senatorial Committee over the past few cycles. And now, Rastetter is getting up close and personal with the presidential hopefuls in full view of the media and other deep-pocketed donors.

He’s also developed his share of business and political enemies in recent years, ranging from environmentalists who don’t like his hog operations to university advocates who don’t like the way his money has bought influence at the state’s public universities, where he leads the board of regents.

Rastetter, whose company has a financial interest in agriculture subsidies and strong land prices, in particular, is eager to insert farm policy into the 2016 conversation, though he is coy about his own policy positions. “It’s not my opinion that matters, it’s the candidates,” he said in a phone interview.

For now, Rastetter is not endorsing a candidate — he says he wants to be a neutral host at his summit. Back in 2011, he tried to get Chris Christie in the race, at one point flying a handful of Iowa heavy hitters out to New Jersey to appeal to the governor in person.

But this cycle, he’s taking a different approach. This time, the candidates will all come to him.

Rastetter pulled a lot of levers to get much of the GOP field to come to his agriculture event. He got help from Branstad, whom he recruited to run for governor in 2010 and for whom he was the top donor. Branstad worked the phones with several of the GOP presidential candidates. The governor personally called Bush — who has not been to Iowa since declaring his intention to mull a 2016 run — and also Perry to convince them to attend.

Rastetter also got plenty of help from Nick Ryan, a major Iowa operative, and his wife Jill Ryan, Santorum’s former deputy campaign manager. The Ryans’ consulting and lobbying firm Concordia Group is organizing the agriculture summit.

Rastetter also has a connection to Nick Ryan’s 501(c)(4), American Future Fund, which pulled in more than $13 million from Koch-backed Freedom Partners in 2012. Rastetter told POLITICO that he donated to AFF in 2008 — to run positive ads in support of then Sen. Norm Coleman — but no longer gives to the group. He declined to discuss undisclosed giving to other political causes.

Election disclosures show Rastetter gave $25,000 to an AFF-affiliated super PAC in the 2014 cycle, but had not given to the PAC since donating $5,000 in 2009 — a drop in the bucket for groups that have spent tens of millions in recent years.

Aside from whatever financial ties exist, Ryan and Rastetter are close allies. Ryan said the agriculture summit was his idea. He floated the concept to Rastetter last fall when the two were at a Hawkeye football game: “We were tailgating and talking politics,” he recalls, pointing out that Iowa hosts lots of forums for presidential candidates, but there’s never been one focused on agriculture despite the sector representing a third of the state’s economy. “It seems like a huge opportunity,” he said. “I thought Bruce was perfectly situated to make it happen.”

But Ryan also disputes the notion that Rastetter is a kingmaker in the state. “I understand how folks could look at him that way,” he said. “What I would say is that over the past several years and cycles… he’s certainly become more active. Much like he is in business, when he puts his mind to something he’s very focused and works very hard and more often than not is successful.”

Meet Mr. Iowa

It’s hard to imagine anyone more “Iowa” than Rastetter.

He was raised near Alden, Iowa, on a 320-acre farm that grew corn and soy and raised hogs and cattle. After dropping out of law school, he returned to his roots and launched a feed business that in 1994 morphed into Heartland Pork, a company he aggressively expanded to become one of the state’s largest pork producers. In 2004, Rastetter sold the company to Christensen Farms, making it the fourth largest pork player in the country.

Having conquered pork, Rastetter then turned his sights to ethanol. He launched Hawkeye Energy Holdings, rapidly growing it into the third-largest pure play ethanol company in the country — helping to pump billions of gallons of corn-fuel into American’s gas tanks — before selling to a Koch Industries subsidiary in 2011. He’s currently the CEO of Summit Group, a diverse company that operates in corn, soy, cattle, international farm real estate and private equity.

Agribusiness leaders point to Rastetter as the quintessential Iowa farm boy success story, but as he’s ascended, he’s also become a controversial figure in the state. He’s loathed by liberal community activists who believe he’s leveraged his money into political power for personal gain.

But, even more, they see Rastetter as a symbol of the intensive, increasingly consolidated agriculture industry that rules and too often pollutes Iowa — an issue that’s come to a head recently as Des Moines’ water utility pledged to sue three ag-heavy counties over allegations farm runoff has overloaded the city’s water supply with dangerous nitrates.

In 2011, Rastetter came under scrutiny after Branstad appointed his brother Brent Rastetter — whose company Quality Ag builds large scale hog facilities— to the Iowa Environmental Protection Commission. Iowa Citizens for Community Improvement filed an ethics complaint alleging a conflict of interests, citing his line of work and the fact that both Rastetters were major Branstad donors. The state’s ethics board later unanimously dismissed the complaint, noting that the position Rastetter held on the commission is one reserved for farmers.

ICCI plans to protest Rastetter’s “corporate ag summit” next week.

A highly-courted donor, Rastetter has steadily and strategically built his personal and political brand over the past several years. He’s upped his disclosed political and philanthropic giving, including more than $2 million to Iowa State University to found an eponymous professorship and entrepreneurship center, $1 million to the state fairgrounds to land his name on the 4-H building and $5 million to the University of Iowa’s football facilities. He maxed out to several top conservative candidates in 2014, including North Carolina’s Thom Tillis, Alaska’s Dan Sullivan and Iowa’s Joni Ernst, and gave $50,000 to Karl Rove’s American Crossroads.

Rastetter has long been known in political circles for his annual summer party, an A-list Republican event complete with pork on a stick that sometimes attracts national conservative figures like Sarah Palin and Bobby Jindal. Last summer, Chris Soules, the current star of “The Bachelor” —who happens to work for Rastetter’s Summit Group as a real estate broker — was reportedly in attendance, rubbing elbows with Marco Rubio and Ted Cruz.

Asked about Rastetter’s annual shindig, Branstad, who’s attended the last several years, gushed that the event is emblematic of Rastetter’s loyal personality. “He is a very caring, sincere individual who doesn’t ever forget somebody,” he said, noting that Rastetter invites a broad range of people, from folks he went to Sunday school with “all the way through the people on Wall Street. Bruce is the kind of person who never forgets a friend.”

Rastetter’s also been stepping more into the public sphere the past couple of years, most notably in 2011 by joining the Iowa Board of Regents, where he’s been the subject of almost constant controversy. Critics slammed Branstad for appointing Rastetter after he gave more than $160,000 to the governor’s 2010 campaign. He’s also come under fire for an Iowa State University-backed development project in Tanzania — which critics argued was a land grab that would benefit his own company —for receiving half a million in no-interest wind energy loans from a university program and for having a ISU researchers conduct a beef study on his own farm.

Ask rural environmental activists what they think of Rastetter and you will get an earful.

Gary Klicker, a native of Davis County, Iowa, blames Rastetter for turning his community into a pork confinement stronghold that now smells of manure after the expansion of Heartland Pork in the late 1990s. He said he ended up with 20,000 hogs within four miles of his house and it’s made him sick — literally. He’s been diagnosed with environmentally-induced asthma and since moved to Colorado, he said. “I could smell the stench from them all the time, no matter which way the wind blew.”

For Klicker, Rastetter is “the poster boy” for everything that’s wrong with big pork. He recalls Bruce came to town and made a lot of promises to the community about good jobs and economic growth. Rastetter took all the business leaders out to dinner at the country club in Bloomfield, Iowa, to help sell pork expansion as a great thing for the community, he said, but Davis County remains among the poorest in the state.

Rastetters’ friends are quick to dismiss his critics, many of whom they argue are simply deeply — and irrationally — opposed to the kind of large-scale agriculture Iowa has mastered.

“There’s always going to be a certain amount of jealousy,” said Branstad. “There’s people who want to move us back to the 1930s and 1940s. They don’t like modern agriculture.”

In the coming days, Rastetter will be narrowing down what questions he’ll ask the candidates on March 7. He said he really wants a serious policy discussion rather than stump speeches, which in past couple of presidential cycles have only really addressed ethanol. While he wants to broaden the discussion, there’s no doubt the candidates will still be pressed on where they stand on the Renewable Fuel Standard.

The would-be candidates and people in their orbit have been calling Rastetter and his team asking for help as they mull their positions on the issues.

“It’s going to make them more substantive in their approach,” said Rastetter. “I think it’s already working.”