British Army veteran Rob Shenton is a middle-aged runner with a taste for the extreme.
In 2009 after the death of his father from lung cancer he vowed that every time he was short of breath he would make it count.
He decided he would run one of the toughest, highest and coldest footraces on earth to raise money for charity.
So far he has done two of the three challenges and is hoping to raise at least £5,000 for military charity Help For Heroes.
He spoke to Forces Radio BFBS presenters Richard Hatch and Verity Geere about his adventures:
Temperatures for the Marathon can drop down to −35° F and this will be only the 16th time the event has been run.
Rob Shenton, 45, was a former army major who served for more than 21 years and saw operational duty in Bosnia, Kosovo, Northern Ireland and Afghanistan.
He has suffered from depression for more than 18 years and despite trying to keep it under control, it became too much for him and eventually he was medically discharged from the army in 2016 with depression and PTSD. Rob told Help For Heroes:
“My mental health has taken me to the lowest levels of despair. It cost me my relationships, friends, property and I even tried to take my life."
The North Pole Marathon is the only certified marathon that is run entirely 'on' water, the frozen water of the Arctic Ocean and is recognised by Guinness World Records as the Northernmost Marathon on Earth.
After preparing for and running the marathons Rob feels like he has his life back on track.
"The North Pole marathon will complete a trio of challenges I started while I was in the army. In a way it will close that part of my life and enable me to move on to the next stage as a civilian and maybe some bigger adventures."