Peterson’s Dothraki entry, which ran to 180 pages, beat out some three dozen others. By 2013, Game of Thrones was one of the most-watched dramas on television, other major networks were clamoring to get invented languages on their shows, and Peterson had enough work to employ him full-time as a language creator. Although it is exceedingly rare for an invented language to take on a life of its own, he has been inundated with translation requests from viewers. He tries to respond to each one, improvising when necessary. Not long ago, one Game of Thrones fan wrote with a special request: Was there a way to say sociology girl in Dothraki? She wanted a tattoo with the phrase. The Dothraki inhabit a world where horses are the primary mode of travel and fire-breathing dragons circle in the sky—a world, perhaps needless to say, unacquainted with sociology. “There is not and will never be a word for it,” Peterson told her. Still, he offered a translation: nayat fin avitihera vojis sekke—“girl who will stare at people too much.”

Learning a made-up language is not easy, and Peterson wants to help actors get it right. He has spent hours on the phone walking them through their lines, syllable by syllable. It can take days to get the pronunciation down. Nichole Galicia, who played a Kinuk’aaz-speaking alien on Defiance, told me she was once given new lines just hours before she filmed a scene. With little time to practice, she was unable to master them all. Midway through the scene, she blanked and blurted out the first Kinuk’aaz phrases that came to mind. “I was saying ‘Happy holidays’ when I should’ve been saying ‘You disgust me and disgrace our people,’ ” she told me. No one on set knew the difference; the director deemed the take her finest performance. Galicia, however, was mortified. She ran to her trailer in tears and called Peterson to apologize for “butchering” his language. “I’m sure it’s worse in your imagination than it actually was on film,” he assured her. “And if it’s dreadful, we’ll dub the scene.” They dubbed it.

The morning after his Daily Show appearance, I met Peterson at his hotel for a language lesson of my own. Fancying myself, like Trevor Noah, a High Valyrian kind of guy, I hoped Peterson might teach me to order coffee (“just cream, no sugar”) in the language. But it turns out that coffee, like sociology, doesn’t exist in the Game of Thrones universe, and so High Valyrian lacks the words I needed to place my order.

I’d have to settle for Castithan, Peterson said, the language of a race of aliens on Defiance who have done trade with humans, and thus encountered the beverage. Consulting a 317-page dictionary on his iPad, Peterson found the Castithan words for coffee (kofya), cream (krima), and sugar (shugara). He scribbled a translation on a piece of paper and read it to me once, at full speed: “Kofya ksa zhulawa, krima ksa fivi, shugara kanwa.” Then came my turn. It sounded easy enough to pronounce, but I started slowly: “Kof-ya ksa jah-lah-wah—” Peterson cut me off. “That’s a u,” he said. “Try it. Zhu-lah-wah.” After a few minutes of repetition and correction, the sentence was still wobbling off my tongue. Peterson graded me: good pronunciation, poor inflection.

Castithan, he said sympathetically, was a “tongue twister”; the Defiance actors had struggled with it too. I was heartened by this—and by something I’d heard him mutter to himself at the outset of our lesson. “I could do it in one of the Defiance languages,” he’d said, as he pondered which language to teach me. “I just don’t speak them very well.”

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