It was a gray day in America when Craig Ferguson left CBS’ “The Late Late Show” in December 2014, a couple of weeks shy of a decade as its host.

Ferguson has not been exactly invisible since. There was a stand-up special, “Just Being Honest,” which aired over Epix in September, and even before his last “Late Late Show” episode aired he was hosting a syndicated game show, “Celebrity Name Game,” which earned him a Daytime Emmy award and has been renewed through 2017.

But neither of those things really showcase what makes Ferguson singular, what set him off from other late-night hosts: the intimate relation with the camera and the audience watching him through it; his improvised monological essays; a readiness to follow an idea wherever it leads. Ferguson’s also had an openness about his failings, including a history of alcoholism that took him to the brink of a suicide (he has been sober since 1992), and shown a lack of interest in promoted products and canned stories, symbolized by the ritual tearing up of his note cards before every interview.

Ferguson was a magician showing you that there was nothing up his sleeve, except that there really was nothing up his sleeve, apart from his arm, tattooed with Benjamin Franklin’s 1754 famous political cartoon, the image of a segmented snake above the legend “Join or Die.”

That legend is also the title of Ferguson’s new History Channel series, a weekly panel show with a historical bent. Premiering at 11 p.m. Thursday, it puts Ferguson back in late night, chronologically speaking, but more important, it lets him run in a way that fans should find satisfying.

“It had a kind of zippy kind of ring about it, and because I got that (tattoo) stamped on when I became a citizen, it just felt right,” said the Scottish-by-birth, American-by-choice Ferguson of the show’s title.

“Better than ‘Historical Discussions,’” he continued, pronouncing the words with an upper-crust British accent. “That would feel a little stuffy.”

Each half-hour episode has a theme (bad medical ideas, worst political blunder, most influential drug, most influential band, greatest Founding Father, history’s biggest frenemies), with six candidates for each title analyzed and argued over by Ferguson and his panel of three — typically a scholarly expert, a comedian and “someone I’ve talked to, liked and respected in the 10 years that I did the late-night show.” Guests in the last category will include Judd Apatow, Courteney Cox, Lisa Kudrow, Joel McHale, Julie Bowen, Jack Black, Jay Leno, Jimmy Kimmel and Chris Hardwick.

“History Channel seemed like an obvious choice,” said Ferguson of his new series’ home, “because if you look at their programming, it’s vague. There are dramas about Vikings or there’s ‘Pawn Stars’ or ‘Ax Men’ or ‘Ice Truckers,’ so it’s a wide brief. I’m talking about history, but I can talk about ancient Egyptian hairstyling techniques or the best bands of the last 40 years; it’s not too specific.”

The format provides just enough structure to give it a distinct flavor and focus without getting in the way of conversation. But as on “The Late Late Show,” he begins with a monologue. And here, as there, he doesn’t work with a teleprompter, just a list of bullet points. (“I don’t want to read it; if I read it, I’ll be reading it.”)

“I think toward the end of late-night as I got … bored isn’t the right word, but as I became done with it, it got a little mad,” Ferguson said of his old late-night show. “I liked the horse and the skeleton” — he refers to the two-men-in-a-horse-suit Secretariat and his robot sidekick Geoff Petersen — “but I think it became a little too much of that. It’s difficult to have a discussion that suddenly turns serious when there’s a pantomime horse in the corner and a skeleton over there; so I started to limit myself in what we could talk about.

“What I felt I had to return to was the ability to have a genuine discussion which could be in turns funny, moving, shocking, interesting, flippant, frivolous and deadly serious, which is by far and away a more interesting set of notes,” he said. “If it was in musical terms, late-night had me playing the chord E, which is a great chord, but it’s not the only one. And I wanted to do an augmented F7. I don’t regret the show or wish to close the door on it in any way. I’m very proud of it, and I loved doing it. But it was the right time to say, ‘That’s enough of that.’”