It was the early 1990s and Carell, now one of the world's biggest comedy stars, was teaching at the Second City improvisational acting school in Chicago. An unassuming student named Nancy Walls caught his eye and, over a period of three months, he worked up the courage to ask her out … sort of.

''Boy,'' he said to her, striving for a tone of nonchalance, ''if I were ever to go on a date, it would definitely be somebody like you that I would ask out on that date.''

''Well,'' the equally bashful Walls replied, ''if somebody like you were to ask me out on a date, I would definitely go on a date with that person who asked me out.''

What followed was an oblique verbal dance about what this encounter might involve - in theory, of course. More than an hour later, Carell finally bit the bullet and suggested to Walls she could perhaps, you know, accompany him on an evening like the one they had just discussed. She said yes to the date and yes to his marriage proposal two years later. Now, they have a son, a daughter and a family business: a 150-year-old general store in the small Massachusetts town of Marshfield Hills.

''It's just a quaint little gathering spot,'' Carell says. ''I think it's important to preserve these places where you can get a cup of coffee, a carton of milk and talk to your neighbours.''

You might even find him behind the counter if you visit around June: ''We go back every summer so I'm there a lot''.

When he's not ringing up groceries, of course, Carell is busy being one of the most successful actors in Hollywood. In fact, he is the industry's ''most reliable'' comic performer, according to The New Yorker, with most of his films grossing at least $US150 million. He also helped make the American version of The Office one of NBC's top-rating shows.

His latest film is The Incredible Burt Wonderstone, in which he plays a once-popular magician who's been usurped by a crass street performer. Co-starring Steve Buscemi and Jim Carrey, it features Carell as the slightly clueless but good-at-heart Wonderstone, replete with a sparkly velvet jumpsuit and the bronze hue of a Florida retiree.

''They promised me the spray tan would stay on,'' he says, ''but when you wake up every morning and your sheets are brown, I think that's debatable. Nancy loved it, as you can imagine.''

As with all of Carell's movies, Wonderstone features some impressive improvised dialogue. It's a talent for which he is renowned but reluctant to boast about, lest it detract from the writers.

Wonderstone also has a narrative Carell can relate to: devoting your life to something you enjoy rather than something you feel you ''should'' do.

As the youngest of four brothers, he saw how hard his parents worked to give them a good education. After graduating, he did what many high-achieving students do and enrolled in law school. Yet a simple question on his application form - ''Why do you want to be an attorney?'' - forced him to analyse his motives.

''I felt I owed my parents a 'legitimate' career,'' he says. ''They'd invested so much and I wanted to do the right thing by them. And becoming an actor did not seem like something normal people actually do.''

Fortunately, his parents did something many would not: they encouraged their son to quit law school and pursue acting. Even if it didn't work out, at least he'd be spared the gnawing sense of regret.

''They actually had to tell me, 'Don't become a lawyer just for us; whatever you choose should genuinely be your choice'. If I took anything away from it, it's that I'll support my kids in exactly the same way … they need to love what they do.''

Small parts in various films and TV shows followed and Carell took every gig he was offered. Then came a job as a correspondent for a little-known program called The Daily Show. His agent was sceptical but Carell felt the new host, Jon Stewart, would make it a success.

Still, the idea he could become a Hollywood leading man was absurd, akin to ''dreaming of being an astronaut''.

''All I wanted was to keep making a living as an actor,'' he says. ''I wasn't kidding myself about having matinee idol looks.''

The turning point was in 2005, when he became a TV star with The Office and a film star with The 40-Year-Old Virgin. A string of hit movies followed, including Evan Almighty, Date Night and Dinner for Schmucks.

Trying to define what makes a particular comedian funny is difficult. In Carell's case, it's even harder given the absence of signature flourishes such as Jim Carrey's rubbery expressions or Seth Rogen's schlubby antics. Often, a look or a word is all it takes; something that betrays his character's struggle to repress his instincts and bite his tongue.

This was never more evident than with Michael Scott, his character in The Office. But having left in season seven, Carell resisted the temptation to return for the final episode, fearful it might come off as an unseemly victory lap. No wonder he has a reputation as the most normal guy in Hollywood.

''We had lunch together on set one day,'' his Dinner for Schmucks co-star Jemaine Clement says, ''and I learned that he likes to stay home on the weekends and wear cargo pants and have pizza with his wife. I hope I'm not giving too much away.''

''Even now, I feel guilty if I turn something down,'' Carell says, hosing down my observation of his box office power. ''Whenever I'm offered something, I always read the script and meet the director. I still appreciate just being considered.''

All about Steve

"He has to do very little to make you laugh. You're waiting to laugh, because his look expresses a certain demeanour — not uptight, exactly, but prone to taking umbrage."
Steve Martin

"Steve is like a Pixar creation, a character you know was designed and intended to be endearing and funny, like a cobbler mouse ... but with a gigantic penis.”
Tina Fey

"When I work with someone, I always try to figure out, 'What's your wound? Who hurt you?' It's easier to write for them if I can figure out the neurosis. With Richard Pryor, who grew up in a whorehouse, you could track it, but I've never been able to figure that out with Steve."
Judd Apatow

The Incredible Burt Wonderstone opens on Thursday.