Mario Rosen­-stock walks out of the Today FM offices, which the radio station shares with Newstalk, in Digges Lane in Dublin, talking about the boozy 12-hour lunch he shared with colleagues at the weekend. He had reason to celebrate. The radio slot Rosenstock fronts, 'Gift Grub', has reached its 10-year anniversary. In that decade, he has firmly embedded himself in Irish popular culture. His take on characters from Bertie Ahern to Roy Keane have taken on a life of their own, the impressions often more recognisable than the people they're based on.

Sitting down to a glass of water in a nearby hotel lounge in a navy shirt with white polka dots, jeans, and a nice watch, the actor, writer and mimic is well spoken, measured, polite, intelligent, engaged, engaging and professional. A few days previously, before the boozy lunch, he and his colleagues gathered in Lillies Bordello for the official anniversary party. Rosenstock performed a new song about golfer Shane Lowry through the medium of a Brian Cowen impression. He shoved some food in his mouth to get the accent right. The head of TodayFM, Willie O'Reilly, introduced Rosenstock, remembering the early days of his tenure at the station, when O'Reilly would often find the actor originally drafted in on a three month contract face down snoozing on a couch. "He doesn't normally socialise," O'Reilly said, to doubting raised eyebrows amongst those in attendance, "he socialises abnormally," he added, to guffaws.

What did O'Reilly mean by that? "What he meant was it's an all or nothing situation, which I have in common with a few of my friends around TodayFM. Not to put to fine a point on it, it's work hard, play hard. And, em, probably taking into account a little bit of overdoing it. I still have to reconcile in my mind if that's a good thing or a bad thing. It's probably not a good thing in the long run, but it's very infrequent. It's, eh, exuberant!" he struggles to find adjectives. Enthusiastic, I offer? He chuckles. "Well, you're using a euphemistic term, now. Em, go wild. You know what I mean? There's a lot pent up in your mind. There's lots of voices going through my head, things you want to write. You have to explode every so often." He pauses for further explanation before settling on a little joke, "What I'm saying is, I should probably really take up yoga at some stage, but it hasn't happened yet. A little bit of abnormal socialising has always been part of the ticket, I suppose."

Rosenstock has calmed down considerably since the hell raising days of his 20s, and now he and his wife of eight years Blathnaid are the proud parents of 21-month- old son Dashiell. "He and I dovetail really well together, when I am going out to work in the morning at ten to six I give him his bottle. We spend a lot of time together as I finish work early in the afternoon and we have bath-time together every evening – 15 minutes of splashing around. That time is sacrosanct to us."

But it is those voices constantly going through his head that have endeared Rosenstock to the public. He has a wide array of characters that spew forth every weekday morning, and have also manifested themselves in hit albums and songs. That channeling of recognisable personalities was always there.

"I remember mimicking from a very young age," Rosenstock says about what they call the start of 'the journey' on reality TV shows. Frustrated with his parents spelling out words so he wouldn't get what they were saying, he would do impressions of his father to make his mother laugh. Drama and tennis were his two loves as a teenager, and rather philosophically he sees a strong correlation between the two, "When it's singles, people are looking at you the whole time. It is a stage. It's a natural amphitheatre, a tennis court. It's almost a stage where you say your line, he says his line, you say your line, he says his line. I realised that was one of the reasons I was attracted to it." Rosenstock (a Liverpool fan) was born in Waterford but spent much of his childhood in Monkstown, and a lot of time as a member of the De Vesci lawn tennis club.

It's that yearning for attention that sparked his eventual employment by TodayFM, although he's still quite mystified as to why he wants such attention, "I have no idea. You've asked a question which that applies not only to me, but to hundreds of thousands of people around the world. A weakness, an insecurity, an inferiority complex, a superiority complex, I don't know. It's one of those presumably latent Freudian psychoanalytical reasons I have yet to find. I don't ponder on it too much." So you don't want to lie down on the couch and talk about it? "No," he says, before continuing rather seriously, "I've recently thought about that though. Not taking therapy, but the value of therapy. I think people in Ireland don't take care for their headspace at all. They regard it as self-indulgent. If you have a problem in Ireland, you drink your face off. Whereas at least in New York, there's decades of an attitude of trying to take care of your mind. People in Ireland go, 'what would you want with that f**king therapy stuff?' But to take care of your head I think would be a good idea. It would mean you are more fit to deal with other people and have more progressive relationships."

Rosenstock's "ten year gig" (as he puts it) came along when he was about to end his life as an actor (his first role was as Willie Loman in a school production of Death of a Salesman, and he is perhaps best known for playing David Hanlon, the alcoholic doctor on Glenroe). He found life as an actor "very dispiriting," with the thing that most irritated him about it being the lack of control over one's destiny.

"You had no effect over it yourself. You have no power. I'm not a person to go with the flow. Subsequently I've discovered people who are successful as an actor are people who can go with the flow. They can go 'I'll be employed her for three months, and I won't be employed for a while, but that's good because then I can take up my yoga again.' You can do nothing to affect your life as an actor. There is nothing you can do apart from sleep with directors," he says, bluntly. "Beyond barging into someone's office and holding a gun to their head and telling them to give you the part, there is nothing you can do. All the people who break in the industry, their stories are all the same. You get a lucky break. How do you that? You have to work. How do you get work? You get a lucky break. It's for the gods."

Yet funnily enough, it was an acting job that made sure he was to be happily stuck in the land of impersonating people. When he was cast in I, Keano, he realised that he might be in the game for the long haul, "being offered the part on the strength of a radio character, and then later on in the year having a No 1 record with the Keane song, I kind of realised that this is what I'm doing now. I am a comedic writer-cum-performer. There was a recognition that I wasn't a guy doing it as a break waiting for my big break in Hollywood, this is just what I'm doing." And is he comfortable with that? "Yes, absolutely. It fulfils you more that you would expect, because you get to work so many muscles and make people happy. The nicest thing that ever happens is when you get an absolute affidavit from someone saying they were in traffic and looked across and everyone was laughing at the same thing at the same time. That kind of communality appeals to me."

Of course, the Gift Grub ride has not been without bumps, most notably a rift between a former contributor to the show. There is no love lost between his main rival Oliver Callan who left TodayFM for RTE, and accused Rosenstock of using his impressions without consent and saying he was denied a cut from Gift Grub CD sales. Rosenstock has always denied the claims, with many people pointing to Callan's Nob Nation on Gerry Ryan's 2fm programme bearing more similarities to Gift Grub than the other way around.

He gets a good bit of attention when he's out, depending on the setting, "if you're in a restaurant in the early evening, you're not going to get people coming up to you. But if you're in Neary's at 11 o'clock on a Friday night, you're definitely going to have four or five encounters – people coming up to you with their mobile phone, and they're like 'leave a voice message as Keano, would ya?'" Does he do it? "Of course I do! To be honest with you, I've no time with people who wouldn't. I think those kinds of people should be taken out and horsewhipped. It's a complete valedictory statement for people coming over and doing that. They're saying they enjoy your work, and all you have to do is do this small little thing. It's hardly a price to pay. I'm always thrilled to do it. I'm not one of those merchants who goes 'I want my privacy'. I think that's, quite frankly, rubbish." He should probably get used to being further recognised, with a pilot for a new satirical RTE chat show in the works to be shot this summer.

So with a strong handshake and some pleasantries, he picks up his keys and heads for the exit, returning to the rest of the day where he goes to bed at half nine in the evening, gets in to work at 6am, and where voices continue to run through his head.