If only the real Samuel L Jackson were half as enthusiastic or engaging as he is on Twitter. On the internet, Samuel L Jackson practically sings. “Daaaaaaaaym!!!” he writes. “C’mon y’all!!” he shouts to some 4.5 million followers. “Be da best MUTHAPFUQQAH U CAN BE!!!” He talks constantly in exclamation marks and expletives, made-up words and spellings (someone once worked out that there are more than 57 versions of the word “motherfucker” on his Twitter account). And he commentates soccer games, snaps amusing selfies, socialises with celebrities (in a picture with Mo Farah: “Bad Mufukkah meets Fast Mufukkah!!” On going to see Ed Sheeran in concert: “This MUFFUGGAH is da real deal!!”). He is the chat-show value version of Samuel L Jackson on a daily stream.

But the Samuel L Jackson I meet is much more subdued. He is slumped on a sofa, feet resting on a coffee table, in a hotel suite at the Beverly Hills Four Seasons, and can barely summon the will to shake my hand when we are introduced. For the first five minutes of our interview he puffs on an e-cigarette and tosses answers at me like he is dealing cards. At one point, when I am not going fast enough, he interrupts.

And he pees. In our 50 minutes together, he disappears unannounced from the suite’s lounge into the bathroom twice for prolonged wees. I don’t know whether to be offended. The first time he does it, we are in the middle of a conversation about Brixton – I had read somewhere that when Jackson arrives in a new city the first thing he does is seek out a “black community”. When we met in early November, Jackson had just made four films in London.

I make the error of asking which black community he visited.

“Where do you think?” he stares at me. “Come on!” he says.

So I locate the nearest area to where I live in southwest London that is famous for its black culture.

“Yeah, Brixton,” he says, like I am playing dumb.

“Oh cool!” I breeze. “I used to live right next door – in Clapham! For years.”

“You used to live near Brixton but not there? Ha!” he laughs. “Why’s that?” And then he swiftly disappears for the pee. But in the distance, bathroom door shut, I hear him grumbling. “You could live in Brixton, you know!” he says. “They wouldn’t mind it!”

I feel it would be quite weird to shout something back over the sound of the pee.

‘At times in their marriage she has felt “abandoned” by him’: with wife LaTanya Richardson and daughter Zoe. Photograph: Peter Brooker/Rex

Oh, he’s a funny fish, Samuel L. And I wouldn’t be the first person to say it. His partner of 40 years, the actor LaTanya Richardson, once said that the problem with her husband is that he is “emotionally disconnected”. Onscreen he is celebrated for his warmth and wit. But when he is away filming, he apparently can’t even bring himself to say he misses his wife over the phone. Richardson has confessed that at times in their marriage she has felt “abandoned” by him.

When I ask him about his lack of affection, Jackson nods. “I have very brief phone conversations. ‘Oh, I miss you!’” he imitates. “No,” he shakes his head. “[We don’t do] that. She’ll say: ‘Oh, I miss you’ and I’ll go: ‘Oh, OK.’’

How can you do that?

“That’s not good enough?” he asks.

Well, it’s not very nice, I say.

“So I have to say: ‘I miss you, too?’ I don’t think you should say things expecting a response.”

He then enacts a monologue: “‘Oh, I love you! I love you!’” Then in his ladies’ voice: ‘Oh, I love you, too!’ ‘You hang up!’ ‘No, you hang up!’ ‘No, you hang up.’ Psssht. Come on.”

So it’s fair to say that when you meet him, Samuel L doesn’t really do niceties. He does not welcome you or say: “Excuse me, I need to go the toilet.” And he does need a bit of ego stroking – after the interview has finished and I listen back, I realise that we don’t really get anywhere until we have talked about his new film. At the mention of Kingsman: The Secret Service – Matthew Vaughn’s comic-book follow-up to Kick-Ass – he noticeably perks up.

“So you’re starring in a very British comic-book film…” I say.

“WELL, IN’T IT!” he roars with laughter, like I have delivered some sort of punchline.

It’s a grain of sand as far as Jackson’s career is concerned. The highest-grossing actor in the world, he has made more than 100 films (all the more impressive when you consider he got his international breakthrough in Pulp Fiction at 46). He is also the only actor to have commanded anything as huge as a nine- picture deal – at 66 he is on his seventh film of this contract with Marvel, which represents just one part of his oeuvre: playing Nick Fury in comic-book films. That was jammy, I say. “I was just trying to figure out how to stay alive long enough,” he nods, starting to warm up.

With all the work from Marvel, he presumably has comic books coming out of his ears. But Jackson says Kingsman (based on an Icon comic) was a slightly different proposition; he wanted to work with Matthew Vaughn. Starring alongside Colin Firth and Michael Caine (he and Caine, who share an agent, socialise together often) was also a draw: “That and the fact that it was sort of comic book meets the spy genre. They take an ordinary kid and turn him into a gentleman spy.”

He says he has always wanted to be in a Bond film. “But I don’t think I’ll ever get to be in a Bond film, so I felt like this was an opportunity to play a really great Bond villain.”

His character, Valentine, an internet billionaire who styles himself on hip-hop (he wears impeccably cool street wear and serves McDonald’s to house guests from underneath a cloche) was an opportunity to create that villain, he says.

How much input did he have, I ask.

“We matched a lot of the clothes to the book,” he says. “But we changed all the colours to make ’em specific for different occasions, and added cashmeres and different fabrics, and we had prayer beads made for each outfit…” He begins to go into extraordinary amounts of detail about the clothing. He’s just getting started.

So how important is clothing, I ask.

“I love clothes. I’m a clothes horse.”

In fact, Jackson says, most of the time he has it written into his contract that he can keep the outfits he wears in films.

So who is he wearing today? “Armani, Armani, Armani,” he says, dissecting a sea of navy blue – a jumper, hat, trousers. “And these?” he says, holding up his feet. “They’re Adidas. Horse hair.” He even lets me stroke them.

On a role: in Die Hard. Photograph: Rex

According to former colleagues, the small details matter to Jackson. He is what they call meticulous: never late, never forgets a line (pity the reporter who accidentally mistook him for Laurence Fishburne in a live TV interview last year) and undergoes a process of preparing for each film by writing a “character biography” comprising so many pages it has to be bound.

When I ask him about the biographies, Jackson, as he is prone to doing, shrugs me off. So I ask him specifically about Valentine. What was in his biography? “The kind of foods that he eats, educational background, parents, the kind of friends he had, the kind of friends he developed, how he started making money, how he made his money, what he did with it…” It seems an inexhaustible list: “What gives him his confidence, how he’s managed to make his way through the world, especially with the fact that, you know, people…”

People, what?

“Well,” he pauses. “You know I chose to give him a lisp.”

Indeed, it hadn’t gone unnoticed. In the film Valentine’s lisp is used to comic effect. But when I ask why he added the lisp, Jackson says it was because of personal experience. “I did the lisp because people tend to dismiss people who have defects. In interesting sorts of ways. And especially, you know… speech defects.”

He gives me his usual shrug. “I stuttered when I was a kid. People laughed at me when I talked. Smart people.”

I had read somewhere that this was why he started saying motherfucker – to overcome the stutter. He laughs. “It was partly that. But I really just started shutting up. I made such good grades they couldn’t keep up.

“But it’s funny. I remember the first time I met Jonathan Ross on TV, and even I was distracted by his speech impediment. I spent more time dealing with that than talking to him. ‘Hi you’re watching the Jonathan Woss show,’” he imitates. “‘Yeah, weawy! Ever had a ’obNob?’”

He explains that on Kingsman he worked with the producer Jane Goldman , who is married to Ross. “And it’s something we talked about a lot. We had a lot of discussion about my lisping. You know, the way Valentine would say things. She would say: ‘No he wouldn’t say it that way!’ And I would say: ‘Yes I would.’ So we would go on like that.”

Stutterers often start life on the back foot. But this theme seems to run even deeper with Jackson. Raised in Chattanooga in racially segregated Tennessee by his grandparents, he was born to an alcoholic father he met twice and a mother he saw sporadically for the first nine years. An only child, Jackson describes himself as shy and bookish. “I was encouraged to read when I was very small,” he remembers. “I was reading by the time I was three or four years old. I devoured books.”

This was, he says, because he wanted to elevate himself through education. But, growing up, he started to develop the stutter. Concerned about his confidence, his aunt, a teacher in Chattanooga, enrolled him in speech therapy and encouraged him to act, casting him in her school plays. Looking back, Jackson says he remembers feeling “loved and encouraged” by his family. “I was very content in terms of that. But I also knew that their desires were as great as mine – you know, for me to get out. Because the only thing I knew growing up was that I was not going to live in that town or place. That was not an option.”

He raises a finger. “They just had to make sure I stayed alive to get out.” He laughs. “Because they recognised the rebel in me. They were like: ‘We’d better watch this boy.’”

So how did his rebellion manifest itself at such a young age?

He shrugs. “Well, I asked a lot of questions. My grandfather was a janitor, so he worked for all these different people who were generally older white men. When I was around, I would answer ’em back.”

He stares at me. “I was one of those direct-stare kids. And young black kids,” he says, “that’s just not what you do. You keep your head down. You answer questions. But I was looking into their eyes and the next thing I know, it was: ‘So who are you? What do you do?’ And my grandfather’s like: ‘Fucking shut up!’ But I’d say: ‘What is that? What does that mean?’ And they would say: ‘Boy, you’re asking the questions.’”

“But I just wanted to know. I just wanted to identify people in this world and what they had, and why I didn’t have it. Why a man who was half my grandfather’s age could call him by his first name and why my grandfather would have to call him Mr Something.”

Screen test: in Captain America with Robert Redford. Photograph: Rex

Jackson did get out. He went to Morehouse in Atlanta – America’s Oxbridge for young black men. To start with, he studied marine biology but switched to architecture then drama and earned himself a reputation for being involved in early battles for racial equality. In 1969 he was charged and convicted for his involvement in a protest in college and suspended for two years. He subsequently got involved with the Black Power movement (he was an usher at Martin Luther King’s funeral), but before long his mother received a visit from the FBI telling her that his life was at risk.

She sent him to Los Angeles. Then, after two years of being employed as a social worker, Jackson returned to college. It was here that he met his wife LaTanya, who moved with him to New York in 1976 – both actors found work in off-Broadway plays.

But over the next decade, Jackson developed a problem with drugs and alcohol. When I ask him about this period – a time spent drinking bourbon and wine from 8am and smoking weed right through to his performances in the evening – he describes himself as a “functioning alcoholic”.

“I enjoyed it,” he shrugs.

What kind of drunk were you?

“Oh…” he has to think. “Fun? I had a great time. According to most of my friends I was fun. But every now and then I’d get that phone call: ‘I didn’t know you felt that way about me…’”

So you were an “I love you” drunk?

“No, I’d say: ‘You an asshole!’” he laughs. “‘Fuck you!’ Then I’d have to explain.”

In 1990 he went to rehab. The story goes that Richardson and their daughter Zoe, now 31, found Jackson unconscious on the kitchen table. He’s been sober ever since.

So what was his last drink?

“Tequila,” he remembers instantly, in the way that recovered alcoholics do. “I got smashed at a bachelor party.”

Do you miss it?

“No. I guess one of my big questions when I got sober was: ‘Am I gonna be fun?’ But yeah, I still am.”

Jackson has said that there is a direct correlation between getting clean and his success. Before he quit alcohol, Richardson referred to his acting as “bloodless”. Certainly, he says, his acting improved. But there’s a sense that working has also become his new addiction. With an average of five to six films a year, Jackson has an astonishing output. But at his age and with his success (let alone money), I say, nobody needs to work at the rate he does. Or do they?

Jackson smiles. “Painters get up and paint. Writers get up and write. I get up and create characters. I like creating. It fuels me. And it’s doing something that keeps me from being me all day.”

If you were you all day, would that be a problem?

“It can be a problem, yes. I’d rather be working.”

In the last year, he seems to have barely taken a break. And for the most part, he has been in London. “I got there in October 2013,” he says, “did Kingsman. Left for Christmas break. Came back in January, left, did another movie, came back again, did the new Avengers, rolled right into the Tarzan movie.”

I spy: with Colin Firth in the upcoming Kingsman: The Secret Service. Photograph: Jaap Buitendijk

Does he enjoy working away?

“Ah, I go in and out. That’s the way it works.”

And he meets people for dinner anyway. “When I was in London recently, I had dinner with Maggie Smith and Michael Caine. I played a lot of golf…”

Who does he play in the UK?

“Chatty Man’s pretty good actually,” he laughs, referring to Alan Carr. “We even played Dunhill one year.”

He’ll continue to play golf now that he’s back in LA (working near a golf course is another clause in his film contracts, along with an electric massage chair), but he misses people, he says. “It wasn’t until I got back here last week and I was driving around that I realised I saw more people in one day in London than in a week in Los Angeles.”

It’s just as well, then, that he’s so busy. Tomorrow he will go to a read-through for his next project, The Hateful Eight – a new film from Quentin Tarantino – in LA.

“It’s gonna be fuuuuun!” he says. “Well, actually, it’s going to be mean. It’s eight very mean people with eight guns.”

How does feel about reuniting with Tarantino?

“Excited! Always.” He flaps a hand. “We talk all the time.”

And, of course, there are more projects. “I tend to insist to my agents that I know the next three movies I’m doing ahead of time.”

Blimey, I say. Do you drive your agents insane?

“Yes I do!” he says proudly. “It’s a lot of pressure finding a job for me.”

But whatever scripts he is given, he says, he will usually find one. “They just give me a bunch of stuff and I’ll pick one and say: ‘Negotiate this deal.’ You know, we make things work. If it’s a good story, I might say: ‘They want me to play this guy. I don’t like that guy. I like that guy. Can I be that guy?’ And they’ll find out.”

“And then,” he adds, “at other times when a movie comes along, it might be a movie I wanted to see as a kid. So with Tarzan, I always wanted to be in that movie. Here’s the chance. Hell yeah! Let me be in that.”

He smiles. “It’s still the thing that drives me. I’m still doing the movies I was pretending to do as a kid.”

He did go to the movies a hell of a lot – according to what I’ve read, he’d spend the whole day there on his own. Did he ever get lonely? It seems to be the common complaint of an only child.

“No, not at all,” says Jackson. “You know, at a certain point, it was time for friends to go home. I lived in a neighbourhood of kids. But there was a time of day when I needed to stop and go read my book. Go into my head world. I didn’t want to run and jump and hear them make noise any more.”

Later, when Jackson’s publicist comes into the room to say we’ve got a final five minutes, this soundbite rings back through my head. “Oh, she’s done!” Jackson shouts, getting up. So I let him go for his quiet time.

Kingsman: The Secret Service is released on 29 January