Barry Phillips, Chairman of local Antrim firm Legal-Island, will be attempting to complete his first ever Ironman at Vichy, France on Sunday.
An Ironman consists of a three mile swim, a 112 mile bike ride and a 26 mile run one after the other.
They must all be completed in under 17 hours.
Barry has never competed in an Ironman before but has been in intensive training for the event for the past 12 months mainly at Antrim Forum Leisure Centre.
Barry said: “I’ve never done anything like this before and will never likely want to do anything like it again.
“It’s a huge challenge but that’s what I usually thrive on.
“I hadn’t planned to do any fund raising around the event but I changed my mind when I realised there’s an opportunity to raise a bit of money here for a really good cause.
“Earlier this year I lost a good friend to cancer and Friends of the Cancer Centre is a wonderful charity doing wonderful work.”
To make a donation go to www.justgiving.com/Barrys-ironman-challenge