Richard Zacks, a left-handed author with a thinning pate, admits to a weakness for the underdog.

And few figures in American history have been less fortunate than William Eaton, the star-crossed hero of Zacks’ latest book, “The Pirate Coast: Thomas Jefferson, the First Marines, and the Secret Mission of 1805.”

Against the backdrop of the Barbary War, when America was at odds with Tripoli and its Barbary pirates, which had declared war on the United States, Zacks’ narrative homes in on Eaton’s real-life, if quixotic, bid to restore the fledgling nation’s honor after the ruling pasha took captive some 300 American sailors and Marines run aground off the coast of Tripoli.

“Most people give it 50 pages in their books on the Barbary wars,” Zacks said in a telephone interview from New York last week. Zacks’ punchy historical retelling, which provides a colorful, blow-by-blow account of the events — with Batman-style intensity — gives it 400-plus pages with notes.

By the time Eaton, a debt-ridden, down-on-his-luck ex-American diplomat, sets out on the nation’s first covert operation to overthrow the Tripolitanian regime, restore the pasha’s exiled brother Hamet to power and liberate the enslaved Americans, he’d already survived a major blow — then-President Thomas Jefferson, who’d authorized the effort, reneged on his official support for the mission, transferring the decision on whether Eaton would be allowed to go to the U.S. Navy.

Against overwhelming odds, Eaton would make his way to upper Egypt to locate Hamet, assemble a ragtag force of European mercenaries and Muslim tribesmen, and with just a handful of U.S. Marines in tow, trek some 500 miles across the Libyan desert to subdue its second-largest city, Derne, on “the shores of Tripoli” — the mostly forgotten victory famously alluded to in the U.S. Marine Corps hymn.

Meanwhile, negotiations led by self-serving American consul general Tobias Lear, a former personal secretary to George Washington, were under way with the pasha. (As early as 1803, the Jefferson administration had authorized the consul general

to conclude a treaty with Tripoli, and if necessary even agree secretly to pay tribute in exchange for peace.) Eaton would be forced to abandon Hamet and the people of Derne and return home once news of the treaty — this month marks its 200th anniversary — reached him.

“In Eaton’s mind, never should an American official ever pay a penny for any hostage,” Zacks said, noting that Eaton would lament: “We gave a kingdom for peace.”

Still, despite Eaton’s betrayal, Zacks cautioned against putting too much blame on Jefferson’s shoulders.

“There’s no telephone back in 1805,” Zacks said, explaining the lack of coordination between the diplomatic, military (a U.S. Naval blockade was also in effect) and covert aspects of Jefferson’s approach to the war.

What’s more, Zacks added, Jefferson’s reluctance to commit the United States to overthrow foreign governments is more understandable in retrospect. “I’m starting to see the brilliance of Jefferson’s point of view,” Zacks said. “If you open the door to create civil wars in countries around the world, the world becomes chaos.”

The book gained an added dimension when Zacks located in the Netherlands’ National Archives a diary by a Dutch diplomat stationed inside Tripoli during the time of the Americans’ captivity — an account that provides fresh insight into the lives of these soldiers and the state of the pasha himself. “When I got that 100 pages in French … it was the best day” of the project, Zacks said, adding that prior to beginning his work he meticulously mapped out a “400-page single space timeline” of Eaton’s life, then took a step back and “structured it into a thriller.” (The approach paid off, as Zacks discovered several quirky, though remarkable, coincidences, such as the fact that Eaton encountered British poet Samuel Taylor Coleridge, struggling with an opium addiction, when he visited the British consul’s residence in the Sicilian city of Syracuse.)

Eaton is hardly the first “underappreciated” historical character Zacks has brought to life on the page. His previous work, “The Pirate Hunter: The True Story of Captain Kidd,” explored the life of Captain Kidd, the “deeply wronged” pirate who Zacks argued was really a privateer commissioned by the British Crown to hunt down pirates.

Then there was “History Laid Bare: Love, Sex and Perversity from the Ancient Etruscans to Warren G. Harding,” an unorthodox look at past sexual practices, which touched on everything from the South American Indian “eggplant penis enlarger” to Joan of Arc’s virginity tests. (The book’s graphic nature inspired a Georgia legislator to introduce a bill — that ultimately failed — in the state Assembly forbidding the purchase of “adult books” by Georgia libraries, Zacks said.)

“The first book was 100 percent sex, the next one was 50 percent, and this one is about 10 percent sex,” Zacks said with a laugh. His wife “thinks this is a very good trend.”

“I love the human detail, I always try to make the scene come alive,” asserted Zacks, a former New York Daily News columnist. “If I found out they had sex with a prostitute … or were offered a 14-year-old Bedouin girl for a sack of rice, I’m putting it in there,” he added, referencing two details in his latest release.

Since the book came out last month, Zacks has been taking his “stand-up history” routine on the road in the family car, a blue Saab, for a tour of New England maritime bookstores. A week or so ago he was in Washington, D.C., at Politics and Prose (he took the shuttle that time). And then there was his appearance on the Don Imus show, which briefly sent “The Pirate Coast” skyrocketing from roughly 4,900 on the Amazon.com rankings to 46. As of last week, however, the book was logging in, “unfortunately,” at somewhere in the less lofty 500s.

For his next project, this writer of “dramatic historical narratives” cryptically said he may turn his attention to an explorer “on the cutting edge of discovering certain taboo things.” And then there’s that novel about 1890s New York that Zacks has been kicking around in his head, but that’s a topic for another day.

As for poor Eaton, after he returned home — although initially feted as a conquering hero and mentioned as a possible Congressional or presidential candidate — he would spend the rest of his remaining six years seeking retribution for Lear, justice for Hamet and forgiveness from his astronomical debts (which were racked up on an earlier diplomatic stint in Tunis).

There was one last thing the “super-patriot” had to do for his country, however.

In an odd twist, Eaton was apprised of infamous dueler Aaron Burr’s intentions to foment revolt against the U.S. administration and create a rival American empire, and despite his animosity toward the president, Eaton provided the first information to Jefferson of his former vice president’s treasonous intentions.

The move almost certainly led to the debt relief from the U.S. government Eaton so craved, Zacks said, but it couldn’t deliver him from his personal demons — gambling and alcohol — or his torment over abandoning Hamet and the people of Derne.

Those battles he ultimately lost.