Who is Caster Semenya? In the two years since the South African won the 800m world title in Berlin, much has been written about her — Semenya the controversial athlete with an intersex condition, a curiosity. But who is the real Semenya? Who is the 20-year-old who became a world champion and then survived everything that followed?

In a hotel lobby in Oslo, where Semenya was competing last week, her agent, Jukka Harkonen, called his young athlete over. "Come here, Caster," he said, encouraging her with a gentle smile. "This lady would like to interview you." Semenya frowned. She reluctantly shook my hand, her slender fingers escaping through mine.

"She is from a good newspaper," said Harkonen. "She is going to do a nice interview." Semenya looked unconvinced. What is a "good newspaper" when journalists the world over had already written about her genitals, pored over her most intimate details? Semenya nodded quietly. She would speak to me after training, but, I am warned, any questions about her gender or 2009 and she will simply get up and walk away. That evening, as we sit down together, Harkonen gives us 20 minutes, checking his watch to time our start.

We hunch forward in our armchairs, me straining to hear Semenya's softly spoken voice. She looks different. Her features are soft, she has beautiful smooth skin, big eyes, high cheekbones. At the press conference earlier that day, Semenya sat next to Norwegian runner Ingvill Makestad. There I watched the other journalists, their eyes flicking between the two athletes, but Semenya did not look out of place in the way that had been suggested when she ran in Berlin. In her ears glittered tiny stud earrings, on her wrist she wore a bracelet covered in diamante hearts and letters that spelled out "V4C", a present from her best friend, Violete Raseboya, an athlete with whom she trains in Pretoria.

The first time I heard of Semenya was in July 2009. A small paragraph in Athletics Weekly mentioned an unknown 18-year-old girl who had just won the African junior championships in a then world leading time of 1min 56.72sec. My eyes popped out of my head. In the busy days building up to the World Championships I forgot about Semenya, but her name reappeared in Berlin, whispered along the press benches.

Within days the story unfolded. A leaked memo printed in an Australian newspaper: Semenya's gender was under suspicion, she had had tests, she was – allegedly – not wholly female. The International Association of Athletics Federations confirmed the story and all hell broke loose. Somehow, amid the chaos, Semenya kept her composure and won the 800m title in 1min 55.45sec, the 13th fastest time recorded by a woman.

As the controversy raged, her rivals questioned her eligibility and Semenya was ushered away from the media. In the weeks that followed, the governing body tried to decide what to do. Eventually Semenya was suspended from competition. Eleven months later, at a tiny meet attended by the world's media in Lappeenranta, Finland, July 2010, she was finally allowed to make her return.

Sitting there in Oslo, I am faced with a moral dilemma. Despite a warning not to ask anything she might deem insensitive, I feel, as a reporter, compelled to push the boundaries, but, as a human, bound to honour my promise. Perhaps Semenya senses my edginess because at each new subject she grows jumpy, waiting to hear what is coming next.

I think of other testing interviews. A fragile Paul Gascoigne, his hands shaking as he tried to light cheap cigarettes; the former West Indies captain Chris Gayle, his mood angry and uncensored; Martina Navratilova, recovering from chemotherapy, touchy, abrupt, raw. Semenya's emotions are within touching distance: scratch the surface and they would come pouring out. But something stops me: not her agent, casting a furtive eye over proceedings, or the timer on my Dictaphone, but something in Semenya's eyes seems to say: "please, don't."

Semenya is best known for running the 800m, but it is the 1500m – or the "one thou five" as she calls it – which is her true love. "Yoh," she says, a typically South African expression. "I like this race more than any other. I like how you can sit back and relax, and wait for the right moment, it's not like the 800m where you just need to go. One thou five, you can watch the race and decide what to do, but 800m is always sprinting."

Semenya scrunches up her face. "The thing I'm afraid of the most with the 800m is injuries. That's why I don't normally like to run in a group, I prefer to be in front, just in case someone pushes me with their spikes. I don't like stuff like that."

So, why concentrate on the 800m? "Because I started running good times. One thou five, I like it, but maybe it's one for the future. Maybe next year, Olympics, I can double up." Like Kelly Holmes? She whistles through her teeth. "Oh! I like what you say. I've met Kelly Holmes, she was in Cape Town. Even her too, she was happy to see me and we talked. She told me I must keep running, I'm still young, she told me I have lots of opportunities to do more."

Semenya's lifelong idol, though, is the Olympic and three times 800m world champion Maria Mutola. "She's still my hero," Semenya says. "I followed her results everywhere she was running, I wanted to be like her. She was running for 21 years, now she's in soccer. We have many similarities." I wait for her to elaborate. Mutola was often the subject of whispers and rumours about her gender, and I wonder if Semenya feels a kinship because of this. "We spoke over the phone," she says, tight-lipped, "but I lost contact with her and now I'm trying to find her again."

Semenya says she never had posters of her heroes on the walls of the room she shared with her sister growing up in a tiny village in Limpopo province. "Actually, I don't like posters. I don't like things of famous people." Now she is the famous person, I say, and she laughs as she tries to make sense of her new identity. "They want to build a stadium in my name, a lot of things — I don't even know. I don't like fame, I prefer to have no profile. But this is not possible for me. This is what I do, so I just have to find a way of being comfortable with it."

At home in South Africa she is a national hero. "Yoh! People are always asking me for pictures, signing autographs, everywhere I go. Before, it used to irritate me but I've learned to handle the situation. I cannot run away, unless I lock myself in my room and never go out."

I wonder how the whole process has been for her parents, approached over and over again by the media to verify the gender of their child, but Semenya says they are happy. "They know it's what I've always wanted [to be successful]. When I was young I wanted to be a professional soccer player, they knew maybe one day I could be something, although they were not expecting anything this big.

"They were surprised when I told them I qualified for the Commonwealth Games in India, and then the world champs in Berlin. They asked me, 'how is it possible that you do that?' I told them, 'you always told me to believe in myself, that's what I'm doing now'. They always wanted me to be happy. Now it's very important for them that I defend my title and not let anyone take it. After that they don't care anymore."

With their young daughter travelling the world and being constantly scrutinised, do they worry? "Yeah, they were worried when this thing," she pauses, gesturing, her arms lost in the indescribable nature of it all, "when this thing started. But they see me now and I'm OK, so why should they worry now? Unless I wasn't OK, then they would tell me, 'Caster, no, don't do this'."

Semenya says she never gets nervous before a race. In the call room, where famously the other runners shunned her ahead of the 2009 final, she likes to put her headphones on and listen to music. "Yoh! Music comes first, doesn't matter what kind, gospel, hip hop. I like Oleseng [Shuping]. He is my favourite." One of the great gospel singers, Oleseng's music is unmistakably South African. The singer died from pneumonia in July last year, around the time that Semenya made her comeback, and it is easy to imagine her listening to his songs: the sound of home, inspiring and uplifting.

She has travelled the world, but Semenya says her favourite food is mielie pap, a maize staple eaten by millions of Africans. "In South Africa I normally eat it everyday," she says. "Pap and vleis [with meat], it's what I like. I don't drink gases, like coke, just juice and water, and I don't drink alcohol. If she could have a dinner party with celebrity guests, who would she invite? She grins excitedly. "Angelina and Brad Pitt! Since I saw the movie Mr and Mrs Smith, I like what they do. About cooking though, I don't know, I'm not good at cooking."

There is something joyous about watching Semenya laugh. Her coach, the fatherly Michael Seme, once said he feared she would commit suicide after everything she had been through. Seme said she had seen it all before. Even as a junior she had been followed into the toilets, intruded upon, as competitors checked whether she really was a girl. To remain on the public stage and compete among the world's best, no matter the headlines and questions, takes extraordinary strength of character.

Born in 1991, three years before South Africa's first free elections, Semenya is not quite a freedom child, but is young enough not to have experienced the horrors of apartheid. For older generations of South Africans, the outside world's determination to categorise Semenya's gender brought back uncomfortable memories of a system that had categorised its people by race. On Semenya's return from Berlin, she was hailed as a hero of the ANC, a symbol of the struggle for self-determination and freedom.

For Semenya the connection is abstract. "You're talking about democracy," she says. "Rights. It doesn't mean anything to me. I cannot say I have rights to do whatever I want, everything I do I report home to my parents. I'm still a kid, I'll always be a kid to my parents. Yes, I learned history at school, I know everything about apartheid. My dad, he bought the books about it, stuff like that. But I just move on with my life. It's completely different for me."

On Thursday, Semenya races against a strong field in Oslo, finishing third in a season's best of 1min 58.61sec. Afterwards, Mariya Savinova, the world indoor and European champion, storms off down the corridor. In Berlin she had sneered at Russian reporters – "just look at her" was her response when asked if she thought Semenya was a man. Other runners were similarly cruel, but in Oslo there is a different feeling.

Semenya chats happily to Janeth Jepkosgei, the Kenyan former world champion who finished runner-up at the world championships in 2009, the two analysing their race, smiling and joking. It is heartwarming to see. While the press wait, Semenya takes her time getting changed. An IAAF official implores her to hurry. "They are waiting for you," he says, exasperated, but Semenya is reluctant. The reporters check their watches – Usain Bolt is running in 10 minutes and deadlines are looming. Eventually Semenya wanders over, her eyes low and guarded. Suddenly she notices me, a familiar face in the crowd. She smiles.

During our interview I ask Semenya what has been the best moment of her life so far. "Ah," she says, "I think when I won the world title. That was the best moment of my life. Things changed, yes, but becoming a world champion, I was never happier before I did that."

It seems an extraordinary thing to say after all she has been through. Can she not imagine a happier time? She smiles and finally responds. "If I win it again I will be even happier."