Every year, thousands of people visit San Antonio to see the place where Davy Crockett and 188 other "American heroes" held off 4,000 Mexican invaders at the Alamo. But today, the Texas city hosts a different sort of commotion. Inside one of the many Mexican restaurants lining the famous River Walk, a middle-aged waitress is suddenly drawn to a distinctive character in an odd combination of hip-hop sportswear and intellectual-looking spectacles. "Señor! Señor!" she calls to John Legend, in town to play a gig at a converted railway station. "Are you in a rock band?!"
Legend, whose mesmeric Get Lifted album combines hip-hop production with classic soul, is not by any stretch of the imagination in a rock band. However, his fame has reached that level where passersby know that he is famous, even though not all of them are entirely sure why. Yesterday, says Legend, he was in a restaurant in New Orleans and had "10 requests for autographs before I sat down".
His enthusiasm may soon turn to weariness at being intruded on, but it might not. Legend insists he has been quietly expecting stardom since the age of "four or five". "As soon as I started singing and playing, I wanted to be doing it on TV," he says with a smile, "and I knew I would."
Even so, it's unlikely that he planned for this level of success. Get Lifted hit number 4 in the US charts. Prince told Legend, "You write songs, nobody does that any more", and the 26-year-old shared a stage with Stevie Wonder. Together, they performed Legend's song Ordinary People - an occasion that the younger man admits he "couldn't dream". The UK has yet to succumb so completely, but there have been two hit singles (Used to Love U and Ordinary People) and appearances on Parkinson.
Legend has spent most of his adult life on the road. He was launched to stardom by Kanye West, who signed Legend to his new label after catching one of his shows in 2001. Back then, though, "he wasn't Kanye West, super-producer", insists Legend. "He was Kanye West, the guy who does hip-hop beats and might be on the new Jay-Z album."
Still, West's patronage opened doors. The pair have toured together and collaborate musically.
"We challenge each other," says Legend. "We really go at it sometimes." They have their differences outside of work, too. Where Legend berated a magazine for "misrepresenting" him as arrogant, West makes self-mythologising pronouncements, the latest being: "I'm the closest that hip-hop is getting to God." Told about this, Legend is initially speechless. "He doesn't say that to me!" he chuckles. "I think he says things to reporters to get a rise out of them. He loves it when the press go crazy."
Legend would never say anything like that because, he says, he's "more measured, businesslike ... There's that element of swagger, but I'm more subtle." Yet he may have inherited West's playful willingness to go against the grain. Contrary to soul music's confessional tradition, he is guarded, preferring to talk about details such as which radio programmes in the UK are playing his new single. He is making some of the most emotionally uplifting soul of the past decade, but insists he has "difficulty expressing feelings". "I don't think I'm an emotional person," he says, amazingly. "I'll go to a funeral and I'll be the one person not crying." But a week ago, in the middle of performing Live It Up (a song about overcoming poverty), something happened. "My voice broke," he sighs. "It was like the strain and the passion suddenly overwhelmed me. I emitted a slight tear."
Legend was born John Stephens in Springfield, Ohio, the son of a seamstress and a factory worker who spent two years in the National Guard. He had a happy childhood, taking up the piano aged four and getting a taste for performance in the church choir. However, when he was 10, his parents divorced and his mother had a breakdown.
"She had a time when she couldn't be around us," he says. "She was kinda ... gone for a while. Mentally, physically, and spiritually." He won't expand further, calling himself a "bottler of emotions".
It's perhaps not coincidental that at around this time he began pouring his suppressed hurt into songs. He started listening to classical, gospel, MC Hammer and his father's soul tunes - similar ingredients, give or take Hammer, to those that make up his songs now - and his mates dubbed him "Legend" because of his similarity to old-school soul acts. Back then, he says, his musical goals were no different. "I try to make it transcendental," he says, "but structured. I have a very mathematical, systematic mind."
Because his family always stressed the importance of education, Legend ended up studying in Philadelphia, that bastion of soul music. But he fell into a job as a management consultant - hardly a vocation for a soul man, but it gave him a good grounding for the business. His schedule in those days sounds draining: he would work all week, gig in the evenings and at weekends, and spend Sundays directing the church choir.
Legend released albums via a website and put up his own posters promoting gigs. Finally, in 1998, he "met somebody that knew somebody that needed somebody". The somebody who needed somebody was Lauryn Hill. Nineteen-year-old Legend played piano on the ex-Fugee's classic album The Miseducation and followed it with sessions for Jay-Z and Alicia Keys.
His life has been a rollercoaster ride since he signed a deal with Sony in May 2004, but he says that much has stayed the same. The gigs are bigger, the restaurants better, but he still doesn't have a girlfriend. His songs dissect relationships: his own longest lasted seven months, which he frets may be a side effect of the family trauma and "always being on the road".
Legend has also become one of American music's most outspoken opponents of the Iraq war. Last year, when few artists were sticking heads above the parapet, he used his website to carry an essay about how a president had "consistently misled the public" and "made America and the world a more dangerous place".
"On the road I kept meeting families of soldiers who had died," he whispers, serious. "It was difficult because I couldn't comfort them by telling them they lost their sons for a good cause. But also the last thing you want to tell them is that they died for nothing."
Against the wishes of advisors, he spelled out his views to his fans. "I felt it wasn't that big a risk and that people would respect me for making a decent argument of it," he shrugs, on a day when American TV polls suggest a majority of Americans now think Bush handled Iraq badly.
Perhaps such incidents are making Legend more relaxed about displaying feelings. Towards the end of the interview, he suddenly grabs the recorder and holds it to his mouth, relishing the "pocket therapy" of talking about everything from his desire for a stable relationship to how he is spiritual rather than religious, pointing out that: "I'm a concrete person who needs proof of all that afterlife stuff!"
His own life now is very happy, although there's probably enough sadness in his story to inspire another set of songs. His mother made a full recovery and his parents eventually remarried, but: "They're divorcing again right now," he says, sighing.
· John Legend's new single, Number One, featuring Kanye West, is released today.