Before he bet big on Donald J. Trump last spring, Duke Buchan III was a mostly anonymous figure on Wall Street.
He was financially successful and played polo, but unlike many of the large donors that flock toward presidential candidates in an election year, he was not a billionaire or a big-name financier.
Poor investment returns forced him to shutter his hedge fund in 2011, although he did sock away enough to maintain three residences — a sprawling horse farm in upstate New York, a home in Palm Beach and an apartment on Fifth Avenue in Manhattan.
Of course there is no guarantee that he will be so rewarded, even though it is widely accepted among Republican money men that Mr. Buchan was an early backer at a time when most of Wall Street was hedging its bets, either wary of being associated with such a fiery figure or predicting that Hillary Clinton would win the election.
And Mr. Trump has proved to be unpredictable in his appointments, often casting aside his most ardent advocates.
Still, that Mr. Buchan is even in the mix highlights the extent to which those on Wall Street who were timely and generous in terms of deploying their checkbook are now poised for an outsize payoff. It is also a reminder that while bankers and traders may now be cheering Mr. Trump as the stock market surges, many of these same people were ducking fund-raising calls in the months before the election.
As president, Mr. Trump has tapped a powerful circle of superwealthy businessmen to advise him, although only a few of them were among his original patrons. In fact, going into the election, his support was insubstantial among rank-and-file financiers, the many thousands of midtier executives in investment firms and hedge funds who are often the financial spine of a winning presidential campaign.
All of which makes Mr. Buchan stand out, despite his attempt to keep a low profile. He declined to comment for this article.
Mr. Buchan first emerged on the Republican fund-raising scene as one of the many who supported Jeb Bush in 2015, when he served on the executive committee of Mr. Bush's political action committee, Right to Rise.
Unlike many of Mr. Bush's supporters, however, Mr. Buchan decided to dedicate his time and resources to Mr. Trump last spring. When the Trump campaign announced last May that it would accept outside money for the first time, Mr. Buchan leapt at the opportunity and, along with his wife, committed $898,000 to the candidate's fund-raising vehicle, Trump Victory — the maximum allowed under federal campaign laws.
Some $10,800 went to Mr. Trump's campaign. The rest was allocated to the Republican National Committee, thus endearing Mr. Buchan to Reince Priebus, then the head of the committee and now Mr. Trump's chief of staff.
In explaining his decision, Mr. Buchan told people that he saw the candidate as a disrupter, a fixer and a builder who would bring business acumen to the White House and upset the status quo in government.
He also told friends that he had tired of the politically correct strictures of the day and was looking forward to a time when Americans can say "Merry Christmas" again, said people who spoke with him about his choice. As a hedge fund investor, Mr. Buchan embraced the candidate's promises to slash taxes and regulations as well.
At a time when Mr. Trump's campaign was struggling and traditional fund-raisers were giving him a wide berth, the donation had a powerful impact, catapulting Mr. Buchan into the candidate's inner circle.
While Mr. Buchan — and his wife, Hannah, a former investment professional herself — had known Mr. Trump socially (his children and Mr. Trump's youngest son went to the same prekindergarten school in New York City), the relationship suddenly became fairly intimate.
They tagged along for the rallies, attended the Republican convention and all three presidential debates and co-led nearly 20 fund-raising events for Mr. Trump. That included one of the first major gatherings held for the candidate in New York City last June.
At the inauguration, the Buchans went to church with the Trumps, sat nearby while he was sworn in and returned to the White House for lunch.
This was heady stuff and a far cry from the farm in Henderson, N.C., where Mr. Buchan grew up. He calls himself a 10th-generation North Carolinian and received his undergraduate degree nearby at the University of North Carolina.
His hunger for a top diplomatic job in Madrid dates back to his junior year in Chapel Hill, when, he has said, a year abroad in Seville in southern Spain transformed his life.
Mr. Buchan, who speaks fluent Spanish, has since described himself as a champion of Spanish culture in all its forms and, as he lays out in detail on the website of his investment firm, he has established a fund in his name to spur the study of Spanish culture and language at his alma mater.
Mr. Buchan started his career as an investor in 1997 at Maverick Capital in Dallas, the hedge fund set up in 1990 to manage the wealth of the Wyly brothers, Sam and Charles, who became billionaires from their investments in the computer industry and other businesses.
There, he had a near brush with regulators. From 1998 to 2000, Mr. Buchan was on the board of Scottish Annuity and Life, one of the many offshore companies that the Wylys established in the 1990s to conduct financial transactions away from the eyes of regulators.
In 2010, the Securities and Exchange Commission accused the brothers of fraud relating to illegal transactions and trades at these companies. Mr. Buchan was not named in the agency's lawsuit, and his spokesman said that he was never contacted by regulators with regard to his professional conduct.
Mr. Buchan decided to strike out on his own in 2001 and set up Hunter Global Investors. The fund reached a peak size of $1.5 billion — a fairly small amount as far as hedge funds go — before experiencing a surge in investor outflows in 2011, when performance suffered during the European debt crisis.
"We have not weathered the ensuing volatility well," Mr. Buchan said in a letter to his investors explaining why he was returning their money.
Since then Mr. Buchan has turned Hunter Global into a vehicle for his private wealth, with one main fund that is closed to outside investors and another that invests in outside funds.
Mr. Buchan and his wife have maintained a robust social presence in Palm Beach and Millbrook, N.Y., that is often anchored by their enthusiasm for polo. Husband and wife often play at the Mashomack Polo Club, which is the hub for the elite horse-playing set in and around Millbrook, where Mr. Buchan has his farm.
But people who know Mr. Buchan well say that making the rounds at polo tournaments, cultivating truffles and heirloom tomatoes at his estate in the Hudson Valley and putting the work in to become a certified master sommelier (while also tending to his diminished hedge fund) is not going to satisfy him.
Going back to the 1990s, when he was a junior investment banker at Merrill Lynch pitching companies and governments in Argentina and Colombia on banking deals, Mr. Buchan has always had a distant ambition to represent the United States in a Spanish-speaking land, said people who have worked with him.
Now all he has to do is wait — and hope.