“The Late, Late Show” host Craig Ferguson is a natural as a chat show presenter. The inspired wit displays Johnny Carson’s sophistication, Jack Paar’s emotional honesty, Merv Griffin’s enjoyment of people, Steve Allen’s zaniness and Groucho’s ability to embrace both the high and low brow. He has reinvigorated the late night TV scene.

But talk show host wasn’t exactly Ferguson’s lifelong ambition. The Glasgow native has been a punk rocker, stand-up comic, actor, director, screenwriter and novelist.

A supporting player for years on “The Drew Carey Show,” Ferguson scored strongly as a guest on various talk shows, but never imagined himself behind the host’s desk. After a parade of entertainers engaged in on-air auditions, he landed the gig as Craig Kilborn’s successor on “The Late, Late Show” in 2005.

“I wasn’t interested in it all until I did it,” Ferguson said prior to a San Francisco stand-up gig. “Talk shows were just something you did when you had a movie or something to plug. But when I did it, I just kind of fell in love with it right away. It got me early. I fell in love with it before it fell in love with me, I think,” he laughs. “It took a while for it to settle. It was a couple of months before we started really flying, I think.”

His boss David Letterman and Regis Philbin were helpful at the outset. But the greatest sage turned out to be none other than Howard Stern. “He gave me a very pertinent piece of advice - you have to, as soon as you can, make it your own. You cannot listen to what anyone else is telling you about what you should or shouldn’t do.

“That actually turned out to be the clearest and most positive advice I got. He was right. You just have to throw out all preconceived notions about it and just own it. Own your mistakes. Own your imperfections. And do it your way.”

Ferguson loves the spontaneity of the format. “You have an idea in the morning, it’s done and on TV by the evening and you don’t have to talk to 25 development executives about - does the guy have a dog or a girlfriend? You just do it and it’s done.”

His interviews are delightfully unpredictable. He doesn’t let guests get away with their usual canned hype.

Like Steve Allen, Ferguson welcomes regulars, “a loose repertory company,” as he calls them. Frequent visitors include Henry Winkler, Betty White, Dave Foley and Tim Meadows. They offer comic commentaries, feigning expertise on a panorama of timely topics.

“That’s been fairly organic. It tends to be people I have a good time with when they turn up. Like Henry Winkler turned up to do a bit and then he had such a good time, he’s become a regular on the show. Dave Foley the same. Dominic Monaghan, as well.”

Ferguson plays a number of colorful characters, including Prince Charles, J.K, Rowling, Angela Lansbury’s detective Jessica Fletcher, Bono, Sean Connery and Michael Caine. Caine enjoys Ferguson’s caricature of him.

“It was a revelation to me that he saw it. He said to me, I’d better be careful, because Connery’s sense of humor isn’t as good as his. But it’s very gratifying when people like that see it. You forget that super-famous people have TVs... but they do.”

Ferguson has toyed with the idea of portraying these characters in his stage shows. “I’m wondering if, at some point, I might do that. But that gets a little more involved, with people and costumes, traveling. And that’s a bit of a logistical nightmare. With stand-up, I just show up in town and do it. With the other stuff, it can get a little bit tricky.”

The opening monologue lasts about nine minutes. A lot of that is Ferguson winging it, sailing off on terrific tangents. “That makes it exciting for everybody, including the censors.”

In the beginning, he read one-liners, but soon transformed the monologue segment, utilizing his own unique madcap sense of irony. “That was part of the growing pains, I guess. You start doing it the way other people have done it and then you say, ‘Well, that’s enough.’ That’s really what happened. It wasn’t that long, only a couple of months before the mold started to break for me. They used to be very long, though. I used to do like 15 minutes, which is too long.”

Much of it comes off the top of his head. “Some nights, it’s maybe only 50 percent or less, the amount of material that’s prepared before the cameras start. A lot of it is just made up. Some days, when I’m tired, then I’ve prepared most of it beforehand. It varies from night to night. But it’s certainly all been that day and all been within the last couple of hours. And most nights, I’d say 25 to 30 percent of it happens when it happens.”

On the road doing stand-up, he can perform a full set with no one looking over his shoulder.

“That helps a great deal, actually. Although sometimes it’s fun to try and negotiate censorship,” says the master of the double entendre. “It can make you more inventive. But it’s relaxing to go and do stand-up. There’s a loose structure and I riff around various subjects. It’s not a new act every night... but it’s not the same act every night either. Lines come and go, subjects come and go, but the shape tends to remain the same... until I throw all of it out and do a new one.

“I do love doing it. There are certain parts of the world where I especially love doing it and San Francisco’s one of them. It’s easy to get to and it’s fun and it’s foggy all the time, so it’s like Scotland. I’m looking forward to it.”

Though no censor monitors him on stage, Ferguson, wherever he’s performing, sets some limits. He garnered much positive reaction when he announced on his show that he wasn’t going to mock the head-shaving, rehabbing Britney Spears.

“That was sort of a sea change in my own professional life, when I thought, ‘You know what? There is a line.’ And it’s a personal line for me. I’m not advocating censorship for any late night comedian.

“My favorite stand-up comedian working at the moment is a guy called Dave Attell. Dave is absolutely horrendous, but he’s the guy who makes me laugh more than anybody else. He would show no mercy towards anyone. But I have stuff that I won’t do. It’s just not for me to do. I keep an eye on that.”

When Ferguson mocks public figures, it’s good-naturedly, not out of cruelty. With Brittany Spears’ erratic behavior again in the headlines, Ferguson broached the subject. But he poked fun at Dr. Phil, who had intruded on the scene, rather than at Spears herself.

Craig Ferguson chats with Joan Jett on "The Late, Late Show."

“In that situation, the obvious target to me is Phil McGraw, partly because I know Phil can handle himself. He’s been on the show half a dozen times and if he doesn’t like what I say, he’ll call me up and tell me. That’s a lot easier for me to deal with than picking on some bipolar, clearly unstable woman. That’s just not right.”

Ferguson mines humor in his own personal travails, including divorce and overcoming alcoholism. But he doesn’t find fun in the pain of others.

“I’m not going to be any part of that. It’s not from a pious standpoint, at least I hope it’s not. I’ve been there. I’ve wrecked that train. And that just ain’t fun. It might look fun to people or for people.

“It smacks of Bedlam to me - you know the English lunatic asylum? In the 1700’s, people would go and laugh at the lunatics, because they didn’t know any better. That’s what that shit looks like to me. I’m like, ‘Oh, no, man, I’m not going to be a part of that. I can’t be a part of that.”

He insists he’s not anxious to be part of the movie world again [Though he voiced the character Gobber in 2010’s animated “How To Train Your Dragon”]. That’s a great loss for filmgoers. Ferguson wrote, produced and starred in “The Big Tease” and “Saving Grace.” He directed, wrote and starred in “I’ll Be There.” All three are very funny, charming, feel-good films.

“I’m not missing that. Movies are great to do, when you actually get to shooting them. But it’s the five years of talking bullshit to utter morons who are trying to get the Afghani television rights or the Canadian internet rights sorted out so you can raise enough money to shoot the damn thing. I just couldn’t take it anymore.”

Though he has set ratings records in his time slot and earned an Emmy nomination, Ferguson doesn’t foresee the sort of decades-long run that Letterman and Carson managed.

“I can’t see doing anything for that amount of time. I’ll do it for a while. I like doing this. I’ve always said, when it stops being fun, I’ll quit. It’s not fun every day - no job is. But when it consistently stops being fun, I’ll quit and figure out what’s next at that point.

“I feel my trump card in this late night game is that I didn’t start doing it until I was 42. I made a living before that and I’ll make a living after it. I’ll do it for as long as I feel that I can contribute something and that I’m doing something that I love doing. But I’m not just going to show up just to show up... because there’s other things to do.”