In June, Harold C. Simmons, a wealthy Texas businessman, sent a $100,000 check to Americans for Rick Perry, a super PAC preparing for Perry’s entry into the presidential race. In December, Simmons wrote another check, this one for $500,000, to Winning Our Future, a super PAC supporting Newt Gingrich.

But Simmons was not done. In mid-January, as Gingrich was headed toward a victory in the South Carolina primary, Simmons wrote a $100,000 check to Restore Our Future, the super PAC supporting Mitt Romney. And toward the end of the month, as Restore Our Future used his money to help bludgeon Gingrich with attack ads in Florida, Simmons sent yet another $500,000 check to Gingrich’s super PAC.

"He generally supports conservative Republican candidates," said Chuck McDonald, a spokesman for Simmons. "I assume he was just trying to be helpful."

Simmons’ contributions — all told, he has given more than $14 million to Republican super PACs so far this cycle — make him the exemplar of a new breed of superdonor in presidential politics. About two dozen individuals, couples or corporations have given $1 million or more to Republican super PACs this year, an exclusive club empowered by the Supreme Court’s Citizens United decision and other rulings to pool their money into federal political committees and pour it directly into this year’s presidential campaign.

Collectively, their contributions have totaled more than $50 million this cycle, making them easily the most influential and powerful political donors in politics today. They have relatively few Democratic counterparts so far, with most of the leading liberal donors from past years giving relatively small sums — or not at all — to the Democratic super PACs.And unlike in past years, when wealthy donors of both parties donated chiefly to groups active in the general election campaign, the top GOP donors are contributing money far earlier, in contests that will determine the Republican Party’s choice of a presidential nominee.

"What unites them? They’re economic conservatives," said Christopher J. LaCivita, a Republican strategist who helped advise Swift Boat Veterans for Truth, a forerunner of this cycle’s super PACs, and in 2008 co-founded another Republican advocacy group, the American Issues Project, that ran advertisements against Barack Obama.

"Most of these guys are serious business tycoons," LaCivita added. "They’ve built something big — usually something bigger than themselves."

Some of the superdonors, like Simmons and Robert J. Perry, a Texas homebuilder, are longtime backers of independent groups that were active in past campaigns, like the Swift Boat group, which in 2004 challenged the Vietnam War record of Sen. John Kerry, the Democratic presidential nominee.

Several of them attend the exclusive, secretive gatherings of wealthy conservative donors hosted twice a year by the billionaire Koch brothers. Many move in the same social or political circles: Sheldon Adelson, a billionaire casino executive who is close to Gingrich, serves on the board of the Republican Jewish Coalition with Paul Singer, the hedge fund executive and a top contributor to Restore Our Future.

Some of the million-dollar-plus donors, however, are relatively new to the world of big-league political giving and appear to be motivated by personal connections to particular candidates. Paul B. Edgerley and his wife, Sandra, for example, together gave $1 million to the pro-Romney super PAC. Edgerley is an executive at Bain Capital, Romney’s former firm.

A few of the megadonors gave through limited liability companies, shielding their identity. One $1 million donation to Restore Our Future came from F8 LLC, a company whose listed address in Utah leads to an accounting firm. A charitable foundation linked to Sandra N. Tillotson, co-founder of the skin care firm Nu Skin, uses the same address. Tillotson was reimbursed by Restore Our Future in July for what appeared to be costs associated with a fundraiser at her New York apartment.

But the superdonors all have one thing in common: They are by definition deep-pocketed, willing and ready to give far more than the $2,500 checks that donors to candidates are limited to writing. Indeed, some of them have almost singlehandedly financed super PACs that support their favored candidates.

Peter Thiel, the co-founder of PayPal, has given Endorse Liberty, a super PAC supporting Rep. Ron Paul of Texas, at least $2.6 million, the bulk of the group’s donations so far. Adelson and his family have contributed more than $10 million to Winning Our Future, the group supporting Gingrich.

"I might give $10 million or $100 million to Gingrich," Adelson said, in a coming profile in Forbes magazine.

The motivation and logistics behind these large contributions remain something of a mystery. Most megadonors and the campaigns they support are reluctant to talk about the hidden scaffolding of high-level political giving. But glimpses of it emerge in public records.

Robert Perry, who has donated $3.5 million to Republican causes in the current election cycle, rarely speaks publicly about his contributions. However, he testified in a 2007 lawsuit that he occasionally got calls directly from candidates asking for money, and other times he decided to write a check after reading or hearing about a promising politician.

Saying that his "habits are to give more aggressively as we go into the election," Perry, 79, said that in addition to supporting candidates on the national level and in Texas, he likes to give to governor’s races in "other states that are not so big so that my contributions can make a difference."

The lawsuit was brought against the Republican Governors Association by a Democratic candidate for governor in Texas, who said the group did not comply with state campaign disclosure rules in 2006. A judge ruled against the association, which has appealed; Perry was not a defendant.

Several of the biggest donors to Restore Our Future, the super PAC backing Romney, share the candidate’s Mormon faith. A quartet of companies connected to Melaleuca, an Idaho-based company that makes nutritional supplements and home care products, donated a combined $1 million to Restore Our Future.

The company is headed by Frank VanderSloot, who is a national finance co-chairman of the Romney campaign and a fellow graduate of Brigham Young University, Romney’s alma mater.

Many of the biggest givers to the pro-Romney super-PAC hail from the world of finance, particularly private equity and hedge funds. Julian H. Robertson Jr., who has given at least $1.25 million to Restore Our Future, is considered one of the godfathers of the hedge fund industry. Singer and John A. Paulson, another million-dollar donor to the pro-Romney group, are also hedge fund titans.

A few of the superdonors are personal friends: Foster S. Friess, the chief donor to the Red, White and Blue Fund, a super PAC supporting Rick Santorum, occasionally spars with Adelson over his support for Gingrich’s super PAC.

"Sheldon’s prime motivation is his love for Israel, which I share," Friess said in a recent interview, saying he had spoken to Adelson recently. "But my motivation is, I owe this country so much."