If you’re Bill Murray, every day is Bill Murray Day.

In St Vincent, Murray is a familiar kind of hero: the lovable gruff, the mensch in grouchclothing. Vincent is a rude boozer who bets on the horses and has got a Russian prostitute (Naomi Watts) pregnant. He’s mean to new neighbour, single mum Melissa McCarthy. But then he starts babysitting her lonesome son and we twig: he’s great, under the grump. The movie plays out like Murray’s greatest hits. He sings slurrily and dances funny, cracks wise and rolls his eyes, a dignified clown, brimful of feeling even at his most brittle. Melfi originally courted Jack Nicholson, but when he passed, Murray said he was interested, if he could tailor the script to his strengths. And Vincent’s emotional journey follows the same arc as Murray’s characters in Groundhog Day and Ghostbusters, Broken Flowers and Lost in Translation. He gets domesticated. The curmudgeon finds salvation in conventionality. “Vincent has got to acknowledge,” says Murray, “that we all have an obligation to more than just ourselves. In this world it plays out as our fellow man. And ultimately something higher – that’s the ultimate we manifest. But the tasks we’re given here are our families.” Yet Murray’s root appeal is not based on this third-act incarnation. Movies may need to end that way, but off-screen, the closer to average Murray gets, the less we want to be like him. It’s the frank and freewheeling real-life guy we worship, the one who rollicks about dressed like a jumble sale, whose irreverence hasn’t been curbed. So why does he connect quite so deeply?