Richard Whitehead is running 40 marathons in 40 days in memory of his friend Simon Mellows, who died in 2005 after contracting a secondary cancer, and as a tribute to Terry Fox who died, aged 22, in June 1981.
He was an amputee and sarcoma cancer sufferer who died as he tried to run across Canada to raise money for cancer research. He never completed his challenge.
Unfortunately Terry got secondary sarcoma and died on his journey - that set a seed in my head to say that sport is not just about winning it is about the kind of impact you can have. It is about the legacy.
Terry Fox had a massive impact on my perceptions of life and where sport really sits.
For him, it was to raise one Canadian dollar for every person who saw him and he has raised over 400 million Canadian dollars - it is a lot of money towards trying to eradicate cancer in the world. If I had 1% of the impact he has had, it would be amazing.
Whitehead is a natural marathon runner but turned to sprinting because there was no marathon for him to compete in at the London 2012 Paralympics. He not only stormed home to 200m gold but also to a world record.
This charity challenge is also a million pound fundraising quest as he hopes to raise at least that amount - through donations and sponsorship of people who want to run alongside him - for the charities Sarcoma UK and Scope.
Paralympic sprint champion and double leg amputee Richard Whitehead has spoken about the difficulty of running 40 marathons in 40 days.
It is the hardest thing I have ever done. It is massive.
To run a marathon every day for 40 days obviously is going to be tough. I am a mentally strong person and I am physically able to do a marathon - hopefully I will be able to replicate that with the support of my team.
This is about giving up my time to hopefully open up opportunities for other people. I am good at running and hopefully I can inspire other people by doing something that I am good at.
Paralympic 200m sprint champion Richard Whitehead has set off on his ambitious run to complete 40 marathons in 40 days for charity, a challenge he has said will be the "hardest thing I have ever done".