It's been 13 years since the screen cut to black on The Sopranos' final scene. Some viewers assumed that a power cut had happened while they watched Tony Soprano, his wife Carmela, and their son Anthony Jr popping onion rings in a New Jersey diner, as AJ's older sister Meadow struggled to parallel park outside. It was a pretty humdrum family setting, except for the growing sense of dread within the audience as the camera gave undue prominence to a shifty man we'd never seen before, throwing Tony's table some casual glances before heading to the bathroom.

With the strains of Journey's 'Don't Stop Believin'' (the jukebox tune chosen earlier by Tony) getting steadily louder, we wonder if this unidentified male is off to retrieve a gun hidden behind the toilet cistern à la Michael Corleone in The Godfather, before wiping out the Soprano family. Or was this sequence of events merely reminding us that a man like Tony, neck-deep in organised crime, would have to look over his shoulder for the rest of his life. As he himself had previously stated to his therapist Dr Melfi, 'there's two endings for a guy like me: dead or in the can'.

Chances are we'll never know exactly what that ending meant. Creator David Chase has refused to give a definitive answer, other than to say, 'it's all there'. But there was always much more to The Sopranos than just an enigmatic ending. Before 1999 (the year it launched in both America and Britain), there were undoubtedly some unappealing central characters on TV, but The Sopranos was the first show which actively required us to invest our sympathy in a sociopathic liar, cheat and killer. But invest we did: he cared about his family, he seemed to be very fond of animals (the ducks in his pool, the horse burnt alive in her stable, the tiny dog sat on and squished to death by a heroin addict), and he was, in the main, considerate towards his friends. Oh, and there was that time his mother and uncle plotted to have him murdered.

Deeply unpleasant individuals (usually men) that we ultimately care about have flowed from our TV screens ever since, in shows like Deadwood, Dexter, Mad Men, Breaking Bad, House of Cards and The Wire. But The Sopranos set the template, and continues to be obsessed over even more so now than when it concluded in 2007. The podcast era has also afforded an outlet to articulate super-fans who dissect each episode in the minutest of detail and go 'deep-diving' into the unanswered questions: whatever did become of the seemingly invincible Russian in the legendary 'Pine Barrens' episode?

Pods like The Sopranos Show, Poda Bing, and No Fuckin Ziti not only break the show down to its bare bones, but have also carried interviews with actors, writers and even costume designers. Arguably, the most exciting podcast development is the imminent launch of Talking Sopranos in which two of the cast, Michael Imperioli (Christopher Moltisanti) and Steven R Schirripa (Bobby Baccalieri), revisit the show episode by episode.

Imperioli and Schirripa, alongside Vincent Pastore who played Sal 'Big Pussy' Bonpensiero, are due to arrive in the UK later this year for the latest leg in their In Conversation With The Sopranos world tour. Already a live hit in Australia and the US, a comedian warms up the crowd for 15 minutes before the three come on to discuss clips, reveal some behind-the-scenes gossip, discuss that ending, and take questions from the audience. This is often the point where things get weird.

'Someone once said to Michael that their son had a heroin addiction, so how did he beat his?' recalls Schirripa. 'Well, he just had to tell them that he wasn't a drug addict, his character Christopher was. And some have asked us questions about the mob, and they've said to Vinnie, "how could you become a rat?" Well, it wasn't him, that was Big Pussy. They get a little confused at times.'

There's no confusion when both Imperioli and Schirripa discuss the merits of their show's boss, creator David Chase. 'Three things make him a singular talent,' states Imperioli. 'He has a really out-of-the-box imagination. He has a tremendous sense of humour. And he has incredible attention to very minute detail, leaving nothing to chance.'

'He was very hands on, and involved in every aspect of the show,' adds Schirripa. 'He was in the writers' room, he was involved in the casting; nothing got by him. David put a lot of people with similar backgrounds together and the writing was incredible, and here we are. The show really holds up 20 years after the first episode aired, and not a day goes by without someone stopping me to ask a question or call me Bobby.'

In different ways, both actors were pushed to the limits at moments across the show. 'I always had a tough time when Christopher got violent with Adriana,' admits Imperioli of some horrible scenes with Drea de Matteo, the actress who played his long-term girlfriend. 'We became very good friends and that kind of stuff is hard; it's a hard place to go to, and every time that happened it was difficult.'

Schirripa describes himself as 'a bit green' when he arrived onto the show and his lack of experience doing drama meant that emotional scenes were tricky for him to pull off. But he had his own teacher on set in the shape of Dominic Chianese whose CV includes the part of Johnny Ola in The Godfather Part II. As Uncle Junior Soprano, Chianese played a senior mob figure with a short temper who ruthlessly cut off relations with his long-term partner after she gossiped about his talent for oral sex. 'Dominic was very patient with me,' recalls Schirripa. 'He's soothing, sweet and nice, not some crazy guy throwing shit around. We talked a lot about acting and he became a mentor to me all those years we worked together.'

Both Imperioli and Schirripa also bonded with James Gandolfini, the beloved actor and activist who died in 2013. 'He gave a shit about people and he was nothing like Tony Soprano,' says Schirripa. 'He wasn't a gangster, he wore Birkenstocks and he loved music. Lots of people thought he would be like Tony Soprano in real life but he wouldn't go onto any talk shows to show them that he wasn't like that. He was shy when it came to that; he didn't think he was interesting enough.'

'He was just a very good friend,' notes Imperioli. 'I acted with him more than I had done with any other actor and probably will ever again; he always gave 100%, really committed himself to every scene and raised the bar for everyone. I miss him a lot.'

There's one memory that Schirripa has of working with Gandolfini that leaves him wincing to this very day. The pair had a big fight scene in a final-season episode after Tony insulted Bobby's wife one time too many during a drunken party. 'That took a day and a half to shoot, and I was extremely sore for days afterwards. This wasn't Steven Seagal, it was a real fight scene because that's how two fat sweaty guys fight.'

The live show is designed to reveal as much of the inner workings of The Sopranos as they are allowed, and some myths might be busted along the way. For example, did Schirripa really wear a fatsuit for the role as Bobby? 'I wore one for the first two seasons, but in the next season I must have got fat enough on my own because they made me take it off. There are two versions of that suit: initially it was a makeshift one and the next year it was a nice costume. I still have that one in my garage in California. Maybe I'll bring it over to the UK.'

In Conversation With The Sopranos has been postponed; the Talking Sopranos podcast has just launched; prequel movie The Many Saints of Newark is due for release in the autumn; The Sopranos is available to watch on NOW TV.