Simon Deng was once a child slave in Sudan, but transformed his life to become a national swimming champion.
Today he lives in the United States and campaigns for political change in his home country of Sudan.
In January 2011, the people of Sudan are due to vote in a referendum on whether the South of the country should get independence.
Simon has just finished leading a march from New York to Washington to put pressure on the US government to make sure that the independence referendum goes ahead.
A referendum was an important feature of the comprehensive peace agreement which ended the civil war between the largely Arab Muslim North and the South, where people follow Christian or traditional beliefs.
Up to two million people died in the civil war, and now the President of Sudan has warned there is a risk of further conflict if key issues between the North and South are not resolved before the vote.
Simon Deng grew up in a small village in the South of Sudan and remembers a childhood of violence only too well.
He saw two of his friends shot dead and other villagers burned alive.
Simon was just nine years old when he was kidnapped and given as a gift to a family in the North of Sudan. He had to do all the domestic chores and says he was treated like a slave.
Later in life he went on to become a national swimming champion, before deciding to move to the United States, where he now works as a lifeguard.
When Matthew Bannister spoke to Simon from New York, he recalled the conditions he faced as a young child in the North of Sudan.