"It's gratifying that people are so passionate about this character I made up when I was a student. Actually I feel like I'm letting them down when they do meet me - because I'm not him. I'm not as interesting a character as Rebus."
Yet he doesn't have fond memories of the first Rebus book, Knots and Crosses.
"That first book was a very dark book. I don't know exactly where it came from. It's overwritten. It reads to me like it was written by a literature student and it was indeed written by a literature student. There's hardly a sentence in it that I wouldn't change if I could.
"It was influenced by Dr Jekyll and Mr Hyde. The reader is meant to think that Rebus is the bad guy, a potential killer. He keeps having these blackouts and he has a room in his apartment that's kept locked and we're wondering what's behind the door. I was in a pretty dark place at that time. I don't remember being very happy when I was a student."
He's unsure what it is exactly about Rebus that keeps drawing readers back.
"I think people like that he's determined; that he's a detective to the core of his being. They like that he's grumpy; a maverick. I like hanging out with Rebus because he's a complex personality and the only way I can find out more about him is to keep writing about him."
Rebus has seen a lot of changes in society, policing and the city he lives in but still drinks at the same bar, The Oxford Bar, a real place, which has become a shrine for Rankin/Rebus fans. Politically Rebus is all over the place - voting once for Labour, once for the Conservatives and once for the SNP.
"I think I cope with change a lot better than he does," says Rankin. "He's a conservative with a small c; he likes things the way they are. That's why he drinks in The Oxford Bar where nothing changes from year to year - not the furniture, the clientele, the layout - nothing."
Rankin's introduced younger characters, Siobhan Clarke and Malcolm Fox, to the series (Rebus is now retired from the police). Despite that, Rebus still inserts himself into investigations.
"Yeah, he can't keep away."
And if Edinburgh comes across like a city ridden with gangsters Rankin insists it's not the case.
"Nah - this is a really safe city. The potential for someone like Cafferty to exist is there but Edinburgh is not a big enough city to have one major gangster. It's got a lot of small-time players. Cafferty I invented to represent all those small time players. He actually owes a lot more to some of the gangsters in Glasgow in the 70s and 80s."
Rankin has co-written a play, penned standalones, short stories and an entire series under the pseudonym Jack Harvey, but returns to Rebus because - "a detective is a really useful way of looking at the world".
"The more recent books have been about Rebus' ageing process. He looks around the world today and it's not making sense to him. It's changing too fast. He doesn't know what his role is anymore.
"Added to that, mortality has tapped him on the shoulder. He's slower than he used to be and he's got health issues. So he's going through the same things his readers and his creator is. As I get older "I ache in the places I used to play", as Leonard Cohen once put it. So I'm dealing with that in my personal experience by giving these issues to Rebus so he, and maybe I, can work them through."
Rankin acknowledges that the clock is ticking. Rebus is now in his early 60s. Rankin 56.
"Can you imagine Rebus at 75 in an old folks' home investigating crimes, racing around in his electric wheelchair? I have slowed the clock down quite a lot and, realistically, there's only so much I can do with him, but who knows? I've no ideas for the next book as yet."
And a book's always kicked off by "one good idea".
"The chronology goes like this. I get a theme I want to explore. I find the plot that allows me to do that and then I ask myself, 'What characters do I need?' So far it's always been that Rebus has been the best character to front the story, but that doesn't mean to say that'll always be the case.
It's gratifying that people are so passionate about this character I made up when I was a student. Actually I feel like I'm letting them down when they do meet me - because I'm not him. I'm not as interesting a character as Rebus
"Maybe next time it'll be Siobhan Clarke or maybe it's a book told from Cafferty's point of view, or maybe it's a completely different set of characters - but I won't know 'til I find out what the story is."
He won't write a novel this year. The time's been set aside to celebrate the 30-year anniversary which brings him to the Auckland Writers Festival next month. If Rebus has been Rankin's road to riches - over 30 million books sold - he's also helped in other ways.
He admits that writing Rebus is a kind of therapy; I suggest that 21 books in, that's a hell of a lot of therapy.
"Yeah, maybe, I needed a lot. I've not had as much as Woody Allen though! I do use Rebus like a punchbag sometimes. I channel frustration and big questions. I give him problems to try to deal with. Being a crime writer's good because you get all that rage and frustration out of your system.
"But at the same time what I do is very childlike. I get to hang out with my imaginary friends and play role-playing games with them and write down fantasy stories. I get to live all these amazing adventures in my head, car chases, gunfights, corruption and sleaze. I get to live in that world but only in my imagination and on paper. That's great and it's why when you meet crime writers we tend to be pretty well grounded. We've dealt with all that dark stuff on the page."
Rankin finds the promo tours hard but necessary work.
"I'm the laziest swine I know. I became a novelist because it seemed like a nice, easy way to make a few quid. You can sit at home in your PJs, get up at midday; you've got no boss. I'd much rather be sitting in The Oxford Bar reading the paper or browsing through the vinyl at a record shop than flying around the world but, hey, it's part of the job, it's just something you have to do, and it's a great chance to discover new record shops and bands."
And on the numbers sold and the money Rebus has brought him?
"I never really know how many books I've sold. I mean, there're so many territories and translations. All I know is I've got enough money in the bank to buy some records and a drink at the pub and that's all I need."
Rankin's a big New Zealand music fan and asks after our own Don McGlashan. When he was here on an earlier trip he saw an ad for Don McGlashan's band The Mutton Birds' 1999 record Rain, Steam and Speed on his hotel TV. He bought the CD and named the 2001 Rebus novel The Falls after a song on it, and met McGlashan soon after.
"I listened to that album a lot when I got home and the songs just grabbed me. And that notion that there must be, like the lyrics say - "a story behind all that". So often stuff that's happening on the surface isn't necessarily the truth . . . so I called the book The Falls."
He's annoyed that his schedule means he'll just miss The Chills' Auckland show next month. He recently wrote a blurb for a forthcoming Chills book - "I love that Flying Nun stuff".
Finally, I ask him if he gets free drinks at The Oxford Bar on account of all the custom he brings in?
"It's never been the case, " he laughs. "I get one free drink per year - at New Year.
What: An evening with Ian Rankin, in conversation with Mark Sainsbury.
When and where: Auckland Writers Festival; Friday, May 19, ASB Theatre, Aotea Centre, 7pm-8.15pm
