He's the golden-hearted former soldier who later today is set to complete a record-breaking 33 marathons in 33 days in a bid to help the homeless.
However, super-fit Mark Conlon insists he won't be hanging up his running shoes any time soon, as he's already eyeing up an even more punishing challenge - a 4,700km ultra-run across Europe.
The 35-year-old - whose previous feats include running 10 marathons in just five days, and more recently 50km a day for 22 days - is raising funds for the Peter McVerry Trust.
If, as expected, he successfully completes the final leg of the challenge today by crossing the finishing line in Clontarf, north Dublin, he will also break an Irish record for the most marathons in consecutive days.
The existing record is 32 in 32 days. However, Mark, who works as a security officer with the Luas, said an even more gruelling challenge is already on the radar in the form of a back-breaking run he's identified across 11 countries.
The colossal E8 European long-distance path spans 4,700km and starts in Cork before eventually winding up in Istanbul, Turkey, after first crossing Britain, the Netherlands, Germany, Austria, Slovakia, Poland, Ukraine, Romania and Bulgaria on the way.
Selfless Mark, from Clondalkin, said helping those less fortunate than himself is all the motivation he needs to push his body to the absolute limit.
"This has been an unbelievable experience and I've been very lucky, because I haven't had one blister," he said.
"Of course it's been tough, but what I've gone through is nothing compared to what people who are homeless on the streets are going through.
"I've seen first-hand how people are suffering, and to be honest that's all the motivation I've needed to get me through this. I'm feeling pretty good now, and if I didn't have to go back to work, I think I'd just keep going," he added.
"But I'm already thinking of what I can do next and it's going to be a lot bigger than this.
"I like the sound of the E8 European long-distance path. It's going to take a lot of planning and we'll need to get a sponsor on board, but I could be taking it on as soon as next year.
"If not next year, it'll be in 2020. And I think I'd like to raise funds for Crumlin Children's Hospital next time."
As part of Mark's latest challenge, he and a colleague also recorded interviews they conducted with homeless people out on the streets - and plan to present their video to the Dail in the coming weeks.
"It's all very well to talk about figures and how many people are homeless, but I've seen the suffering first-hand and now I want the politicians to see exactly what these poor people are going through," he said.
"It's about trying to highlight the human side of this crisis."
If you wish to donate to Mark's fundraising campaign for the homeless, check out idonate.ie/marathonadayforpmvtrust.