A big, slavering, hyperactive golden lab. A dog called Marley. Grogan's memoir Marley and Me, about the yellow dog who barrelled into his life and stole his heart, has sold six million copies worldwide. It is published in 36 languages and has now been made into a movie starring Owen Wilson and Jennifer Aniston as Grogan and his wife. Like it or not, he will always be associated with That Dog.
Grogan, 51, a former journalist, is at peace with that, even if he is still slightly bemused by its success. Speaking as his second book, his childhood memoir The Longest Trip Home, is published in the UK, he says: "Marley and Me was a book I was proud of and believed in, but I thought it would just have a modest audience because it is such a personal story about my marriage and my family. It has been one surprise after another."
John and Jenny were newlyweds living in Florida when they decided to buy a puppy. But soon their golden, wiggly bundle morphed into a 98lb destruction machine eating everything in its path: sofas, underwear, a pregnancy test strip, an 18-carat gold necklace (Grogan picked methodically through Marley's deposits for four days until it reappeared). Marley is boisterous and unpredictable. Thunderstorms reduce him to a nervous wreck. He is expelled from obedience class.
But he is also, to Grogan at least, irresistibly loveable. His capacity for devotion to the Grogans and their three children is boundless. When Jenny suffers a miscarriage, Grogan is shocked to see his out-of-control lab-rador sitting quietly with his head in her lap while she weeps. He is one man's best friend.
Grogan, a columnist on the Philadelphia Inquirer, had for years contemplated ideas for "serious" books: famous murder trials, social issues, Government policies. He gradually came to realise that the story he wanted to write was "literally, at my feet". When Marley died in 2003, he wrote a moving column about him. The next day his inbox overflowed.
Marley and Me went from an unsigned manuscript (Grogan says his proposal was initially rejected by 11 agents) to a publishing phenomenon. It spawned a genre – the pet memoir – which could rival the misery memoir in its popularity. It's a winning mixture of "world's worst dog" anecdotes and gentle, self-help messages about family values.
Grogan is adamant that Marley and Me is not "a dog book". "It's the story of the journey we make as family units, with dogs as part of that. I think Marley is also a metaphor for things that come into our lives that challenge us and either make or break us. In our case, it was this big, crazy dog. I guess in the ordinariness of my life I stumbled on something universal.
"I have to say it was all quite accidental. I didn't sit down and have this brilliant image of this universal story, I just opened my heart and let this tale that was inside of me spill out."
And that's the other secret of Marley and Me: its honesty. Grogan doesn't spare his own blushes, and is frank about his family's hard times, refusing to alter names or details. "Had I known when I was writing it that there would be more than six million copies in print around the world, I might have thought more seriously about self-editing," he says. "But, really, as a writer, I believe that if you're going to write about your own life you need to do it as honestly and candidly as you are capable."
Now, that story is finding an even bigger audience. The movie Marley and Me, directed by David Frankel (The Devil Wears Prada), came out at Christmas in the US and went to number one, and is out in this country next week. Did Grogan worry that the movie moguls would change his story?
"I was a consultant to the script writers and I felt I was heard through that process. I think the film was made respectfully; I think it's a good reflection of the book. It's not exactly my book and it's certainly not exactly our lives – you could say it's a stylised, slightly fictionalised version of our lives – but I think it gets to the larger over-arching truths of our life experience. It rings pretty true, actually."
Grogan and Jenny spent a week on set in Miami with the cast, crew and 22 golden labs who play Marley at different stages of his life. They have a cameo in the dog obedience class. "It was really an out-of-body experience. We're in a scene where we're pretending to be other people, while Owen Wilson and Jennifer Aniston are pretending to be us, and there's a dog pretending to be our old dog. I had to keep stopping to get it straight: who's really who? Who am I?"
It's "flattering", he says, to have himself and his wife portrayed by two of the hottest actors in Hollywood. "Right from the start, one of the first actresses I thought of was Jennifer Aniston. She is so beautiful and really has that girl-next-door charm, and she's funny and my wife is funny. I thought it would be a good fit and it was. I probably wouldn't have thought to pick Owen Wilson, but after a few minutes on the set watching him playing me, I knew he was perfect."
After filming, producers gave them Woodson, the lab who played Marley as a puppy, to join their other labrador, Gracie. "Woodson has got some of Marley's spirit. He's pretty mischievous. He ate a couple of television remotes, chewed up my glasses, bit through a cell phone – classic Marley behaviour. The difference is he's calmer, he'll settle down. He stole my father-in-law's hearing aid and ran off with it."
I tell him it sounds like the gold necklace all over again. "Fortunately he didn't swallow it. We prised his mouth open, got it out, and I think it was still working."
Though he is clear that Woodson is not replacing Marley – "other dogs can succeed him, but he was one of a kind" – it's beginning to sound like the basis for a sequel. But Grogan was clear that he didn't want to write the same book over again.
"I was keenly aware that everybody would have loved for me to do a close sequel or a spin-off to Marley and Me. If I'd had a legitimate story that I'd wanted to tell based around a dog, I would, but I had told the story I wanted to tell. I didn't want to manufacture something just because it would be commercially successful."
In fact, even as six publishers were bidding for Marley and Me, another story was unfolding. Almost at the same time he got the news of his six-figure book deal, he got a phone call from his father telling him that his leukaemia, diagnosed two years before, had become acute.
"It was a rollercoaster. Hour to hour I went from ecstasy over my first book deal, to feeling heartsick about my father's health, worrying about him." It was the beginning of another journey, and another book. While The Longest Trip Home strikes a similar balance to Marley and Me – it is funny, poignant and honest – it is very different. Though there is a dog in the story, he barely features.
It's the story of a boisterous, happy childhood in Harbor Hills, Detroit. There are childhood pranks – altar boys swigging communion wine, a teenage attempt to grow marijuana – and he is disarmingly frank about his early attempts at romance (a clinch with a girl with braces leads to a dramatically cut lip). It is also a loving portrayal of his parents: playful mother and stolid, practical father.
The more serious aspect of the story is about how he overcame his parents' disappointment at his rejection of their Catholic faith. He had fibbed about attending mass for years, but when he married Jenny, a non-Catholic, and they decided not to raise their children within the church, his parents were quietly devastated, and it threatened to create a permanent distance in their relationship.
"It was as if glass walls had come down between us; we could still see each other but we couldn't really have the closeness that we had had. I knew I needed to fix that and I knew it would be painful to try to correct, so I kept putting it off." His father's phone call reminded him that he had a deadline, and they were quietly but movingly reconciled before his death at the age of 89.
"Because for so long I had led them to believe something that was other than my reality, it was very painful for them, but we got through that. I made that trip home and had a wonderful reunion with them, said the things I knew I needed to say, heard what my dad wanted to say. We really felt that we'd come back together, found a place of mutual respect and admiration."
He says writing the book was a "journey of discovery", and one which led him to admire his parents deeply, but adds that he could not have written the story while his father was alive. "I felt the need to write it honestly and I would have been too concerned about it being painful for him". (His mother, now 92, suffers from dementia.)
He is aware that, as he was reflecting on his own upbringing, his own three children, Patrick, 16, Conor, 15 and Colleen, 12, were beginning to find their feet in the world. "I'm now on the other side of the equation; I'm the father, I'm trying to impose my values on my sons and they're trying to become their own people. One of the things that I learned from my parents that I didn't want to repeat was being too unequivocal about imposing my will on them.
"Yet though I ended up rejecting many of the mechanics of (my parents'] religion I think they clearly left a strong moral imprint on their children, and I'm trying to share that with my children too."
Although Marley has made him a millionaire, Grogan works hard to stay grounded. The family has bought an 18th-century farmhouse with 18 acres, but they remain in the same small Pennsylvania town, close to their former home where Marley is buried. The children continue to go to the same school, and apart from playing football with Owen Wilson on a movie set, are largely untouched by celebrity.
"Visiting the movie set and going to the premiere in Los Angeles was very exciting, but I was very aware that we were visiting that life. It was a great experience and exciting and fun and something we'll be talking about for the rest of our lives, but I also realise that's not me, that's not where I belong."
Grogan himself says he knows where he belongs: behind a desk, writing. Since quitting his day job as a journalist two years ago, he says he's had more ideas for books than he's ever likely to complete in his lifetime. He is in that most enviable of states for a writer: able to write whatever he wants. "The gift of freedom," he says. "That's probably Marley's biggest gift to me." sm
• The Longest Trip Home is published in hardback by Hodder & Stoughton, priced 16.99.
• Marley and Me is out in cinemas on general release from Friday, 13 March.