Bob Odenkirk as Jimmy McGill, on his way to becoming Saul Goodman, in Better Call Saul. Credit:Stan Sceptical though they might have been, "they kinda took the leap with us, and we're so glad they did, because the show has taken turns story-wise that we would never have guessed at in those early days". The original idea, he says, was for "a straight-out half-hour comedy. Maybe it'll be Saul sitting in his office in front of the American Constitution on his wall and the Styrofoam columns on either side [a staple scenario in Breaking Bad]. And interesting, quirky people will show up every week with legal problems and he'll solve them. That was the original pitch." Three seasons in, Better Call Saul could hardly be further from sitcom territory. There are laughs to be had, but this is primarily a dark moral drama in which we follow the transformation of Jimmy McGill from a guy who works in the mailroom of his brother's law firm while secretly putting himself through law school at night, into Saul Goodman, whose quick wits and ethical slipperiness lead to him working as legal adviser to the drug cartels. "We love putting as much comedy in our dramas as possible but at the end of the day we're one-hour drama guys," says Gilligan.

When a Breaking Bad spin-off was first floated, Jesse Pinkman (Aaron Paul) was the first character who sprang to mind. Credit:AMC Breaking Bad started dark, with high school chemistry teacher Walter White (Bryan Cranston) being diagnosed with cancer and turning to crime as a means of ensuring his family's financial security after his death. He starts by cooking meth with the aid of drug-addicted former student Jesse, is co-opted by major drug kingpin Gus Fring (Giancarlo Esposito) to make his unusually pure product in an industrial drug lab, and then establishes himself as a drug lord in his own right, known as Heisenberg. Only in his final moments does Walt find some form of moral redemption. Better Call Saul, by contrast, started with more than a faint echo of the sitcom it might have been. Set several years before the events of Breaking Bad, it finds a younger (though not necessarily younger-looking) Jimmy desperately seeking the approval of his older brother Chuck (Michael McKean, still perhaps best known as David St Hubbin in This Is Spinal Tap), who is determined never to grant it. Wrapped in a silver-foil space blanket and huddled in his darkened house, Chuck, meanwhile, struggles to deal with his "allergy" to electro-magnetic radiation, which may be a figment of his possibly decaying mind. Jimmy McGill (Bob Odenkirk) with his brother Chuck (Michael McKean). Credit:Stan But after three seasons and 30 episodes, Better Call Saul has outgrown those cartoonish origins as it inches ever closer to the chronology of the show that spawned it.

"If you picture Better Call Saul as one circle and Breaking Bad as another circle, in a Venn diagram sense there is more of an overlap between the two circles," Gilligan says. "As Better Call Saul progresses, it's becoming more Breaking Bad-like. We didn't set out to do that, it's just turned out that way." Saul Goodman in his Breaking Bad incarnation. Credit:AMC As Better Call Saul progresses, it's becoming more Breaking Bad-like. We didn't set out to do that, it's just turned out that way. Vince Gilligan They chose Saul for the spin-off not because he was their favourite character, "because honestly he was not". He seemed to present more opportunities for storytelling than, say, Jesse or Hank (Dean Norris), Walt's policeman brother-in-law. "But little did we realise he was going to be as rich and complex a character as he has become," Gilligan says. Kudos for that goes to Odenkirk, who was primarily known as a comedy writer and performer before. Now, he says, the world can see "he has so much more range than folks ever knew".

Odenkirk as 'Gene', the post-Breaking Bad iteration of his character. Did Gilligan know he had that in him? "I don't know how to answer this without sounding insulting to Bob, but I don't think any of us knew he was going to be as good as he is. We thought he would be funny and interesting to watch, and that we would write to his strengths, most of which we thought would be his comedy chops. And then when we started the show he started acting and acting and suddenly we realised, 'My God, this guy can really go dark, and he can go sad, and he can do all the dramatic things we could ever possibly want from him'. Kim Wexler (Rhea Seehorn) is the character Gilligan would most like to see in her own show. "So the short answer is we didn't know just how good he was, and now that we do, we come up with as much dramatic stuff as we possibly can in order to challenge him because he always rises to the occasion."

There's plenty more story to come from Jimmy as he morphs into Saul, and there are hints of a third iteration – the post-Breaking Bad character we glimpse in the black-and-white sequences that have started each of the show's three seasons. "He looks a lot like Jimmy McGill or Saul Goodman, except he's got the name tag Gene and he lives in Omaha, Nebraska, and he lives a pretty dreary life," Gilligan says. Vince Gilligan, creator of Breaking Bad and co-creator of Better Call Saul. Credit:ACMI That could be fun to explore down the line, but knowing when to quit is important. "We want very much to figure out the point where we will have overstayed our welcome, and we want to end right before we get to that point. We want to end on a creative high note." Breaking Bad, it is pretty much universally agreed, judged that point perfectly. And while Better Call Saul hasn't enjoyed the same level of popular success, it's fair to say the critics have given the thumbs-up to the idea of a spin-off, and the choice of character to carry it. So what about repeating the trick? When Saul – or Gene – inevitably reaches his endpoint, what chance of another spin-off, and who would it be about?

"I gotta tell you," he says, chuckling at the prospect. "Kim Wexler." Jimmy's legal offsider and sometime girlfriend is played by Rhea Seehorn, whom Gilligan says is "the find" of the series. "She can be hilariously funny, she can be absolutely moving. She can do anything, she just has this astounding range. "Personally, as one of the first two fans of Better Call Saul, I want to know more about Kim, I want to see and learn more about her. "If we were to do another spin-off it would be the Kim Wexler show." Better Call Saul streams on Stan. Vince Gilligan is the headline guest of the inaugural Series Mania television festival at ACMI, July 20-24. Entry is free and open to the public, but bookings are advisable. Details: acmi.net.au/series-mania