“The gentle reader will never, never know what a consummate ass he can become until he goes abroad,” Mark Twain famously warned in his 1869 travel memoir The Innocents Abroad . The humor-packed travelogue, currently celebrating its 150th anniversary of publication, was the author’s first book and his best-selling title during his lifetime. It described, with characteristic sarcasm, the young writer’s inaugural trip overseas in 1867—a five-month tour of Europe and the Holy Land—and a period when he often felt like an uncouth American dunce.

Twain’s local guides on this excursion only heightened the scribe’s inferiority complex, and so he settled the score on the printed page. Among other jabs, the author nicknamed every guide with the all-American alias of “Ferguson,” completely writing off their actual identities. One, however, was notably spared the sardonic misnomer treatment: an unnamed African-American who led Twain and his fellow travelers through the art and architecture of Venice.

His trip began just two years after the end of the Civil War, a fraught time when it would have been easy for the Missouri-born Twain (who grew up in a slave-owning family) to poke fun at this guide, the son of an enslaved South Carolinian who self-emancipated himself when brought to Europe by a white American. Twain had the opposite reaction instead, describing his guide with utmost respect.

“The guide I have spoken of is the only one we have had yet who knew anything,” Twain reported in the Venice chapter of the book . “He is well educated. He reads, writes, and speaks English, Italian, Spanish, and French with perfect facility; is a worshiper of art and thoroughly conversant with it; knows the history of Venice by heart and never tires of talking of her illustrious career. He dresses better than any of us, I think, and is daintily polite. Negroes are deemed as good as white people in Venice, and so this man feels no desire to go back to his native land. His judgement is correct.”

Twain’s admiration for this still-unidentified guide—and brazen statement that he’d be better off in egalitarian Italy than in the United States—signaled a change in the writer’s views and willingness to voice such opinions publicly. When a young Twain left his hometown of Hannibal, Missouri, for New York in 1853, for example, he wrote his mother in a letter that “I reckon I had better black my face, for in these Eastern States niggers are considerably better than white people.”

A few years later, Twain served briefly in a Confederate militia . His description of the guide in The Innocents Abroad marked Twain’s first depiction of a sophisticated and accomplished black person in print., and he’d later repeat similar views in the American classic novels that followed his breakthrough fame from that book.

“One would be hard pressed to find as glowing a depiction of an educated black person in American letters during this period,” says Shelley Fisher Fishkin, an English professor at Stanford specializing in Mark Twain and marginalized voices in American literature. “It is the first time Twain depicted an educated and cultured black person in print, and the guide is so superior to all of the other guides in the book that the difference is truly striking.”

Twain’s description of the African-American guide was a major statement in post-war America and also personally meaningful for the writer. “Twain's real interest in the issue of civil rights for African-Americans was sparked by his encounter with the guide,” says Paul H.D. Kaplan, an art history professor at SUNY Purchase who has reviewed hundreds of 19th-century travel books in an effort to identify the Venetian guide and author of forthcoming book Contraband Guides: Race, Transatlantic Culture, and the Arts in the Civil War Era .

Fishkin agrees with Kaplan that it was important for Twain to meet this man. According to her, prior to meeting this guide, Twain had not encountered an African-American that “possessed the kind of knowledge traditionally valued by Euro-Americans.”

“Twain may well have rejected the racist idea of a hierarchy in intelligence by the time he left for Europe—but the guide would become Exhibit A of the potential intellectual equality of the races, an idea that Twain came to believe ever more firmly as his life went on,” Fishkin explains. “Twain did not need to go to Venice to imagine black intelligence. But he did need to meet this guide to see it in action in such a cultured and refined way.”

On the very same day that Twain submitted his manuscript of The Innocents Abroad to his publisher, he also wrote a longform newspaper column for the New York Tribune revealing that he now believed in extending U.S. citizenship to Chinese immigrants and African-Americans. “From being ‘appalled’ at this idea,” notes Kaplan, “he was now in favor of it.”

Twain’s article stated, in reference to a treaty extending legal privileges and immunities to Chinese subjects in the United States, that “I am not fond of Chinamen, but I am still less fond of seeing them wronged and abused.” He went on to write, “The idea of making negroes citizens of the United States was startling and disagreeable to me, but I have become reconciled to it; and being reconciled to it, and the ice being broken and the principle established, I am now ready for all comers.”

He advocated for correcting the systemic abuses against the African-American community for the rest of his life, writing an editorial condemning the lynching of a black man in 1869, and began a meaningful friendship with leading abolitionist Frederick Douglass that same year. Twain also penned an 1874 article for The Atlantic Monthly (the writer’s first of many for that publication) recounting the poignant life story of his African-American cook, who was born enslaved and had been separated from her children. Later in life he helped fundraise for Tuskegee University, a historically black university in Alabama. Alongside this advocacy activity, Twain continuously used his writing to campaign for social reform.

That wasn’t the case during his early career, though, before The Innocents Abroad . According to some Twain scholars, he had a track record of ridiculing African-American characters in his writing of the early 1860s, but this stopped around the time of his visit overseas. The year 1867 also marked when he stopped using the n-word, unless it was in quotation marks (indicating it was a term being used by others and one the author didn’t condone). “When he uses the n-word after that time it is almost always in a context that is ironic or sardonic, or portraying someone else’s dialect,” says David Sloane, an English professor at the University of New Haven and a Mark Twain scholar.

Proofs for The Innocents Abroad also reveal that Twain wrote and then changed every appearance of the n-word to “negro,” the term that he applied to the Venetian guide.

The n-word didn’t disappear from Twain’s writing altogether, though. As many have pointed out, the racist epithet appeared over 200 times in Adventures of Huckleberry Finn (1884), albeit voiced by a narrator who wasn’t Twain. This remains controversial, causing some libraries and schools to support banning the book . Other readers believe the condemnation of Huckleberry Finn to be a misguided interpretation of the writer’s intent .

“Twain is not willfully buttressing racism here,” wrote Harvard law professor Randall Kennedy in his 2002 book, Nigger: The Strange Career of a Troublesome Word . “He is seeking ruthlessly to unveil and ridicule it. By putting nigger in white characters’ mouths, the author is not branding blacks, but rather branding whites.”

Around the same time Twain wrote Huckleberry Finn , he also penned a letter of introduction for his neighbor, African-American still life painter Charles Ethan Porter, to use for access to artists’ studios and schools in Paris. Porter and Twain met when they were both living in Hartford, Connecticut, in the early 1880s; the writer bought a floral still life by the painter that he hung prominently in his dining room (a design feature now replicated at the Mark Twain House & Museum ).

“Without money or moneyed friends [Porter] has fought his way steadily to a good & substantial place in the esteem of the people here,” Twain wrote the letter. “By sheer force of talent & patient diligence in the study & practice of his art, & he carries with him introductory letters from citizens of ours who do not give such things lightly.”

Twain may have wanted to help Porter avoid the humbling experience—one he knew firsthand—of going abroad and becoming a “consummate ass.” But he was also supporting his painter friend, in a small way, pursue his love of art overseas, perhaps remembering the cultivated African-American guide he had met in Europe over a decade earlier.

Meeting the Venetian man of South Carolinian descent challenged the writer’s prejudices about the intelligence and capabilities of African-Americans, and upon returning to the United States he repeatedly corrected this error, in print. The memory of the guide stayed with Twain, long after other details of his momentous trip had faded.

More than a decade later, when Twain next returned to Venice as part of a voyage recounted in his book, A Tramp Abroad (1880), it was clear he hadn’t forgotten this guide—although it seems they didn’t meet again. “Though Twain was ambivalent about the value of famous European pictures (he once suggested that ‘Old Masters’ was short for ‘Old Masturbators’), what the guide told him about Titian and Tintoretto stayed with him,” writes Kaplan . He remembered, word-for-word, how this erudite guide had described Tintoretto’s large-scale Paradise painting in the Doge’s Palace, as ‘an insurrection in Heaven.