Dorset man Butter is currently in Mauritius ahead of marathon number 64 and has 132 to go to finish his 5,130-mile challenge, Reuters reported.
His epic started in London in January and has so far seen him from cross the globe from Canada to Swaziland, staying with locals and training with running clubs he meets along the way.
The inspiration came from a chance encounter with fellow runner Kevin Webber, who has been running marathons himself since being diagnosed with terminal prostate cancer in 2014.
“I didn’t know Kevin but I was staying in the same tent as him and we got on really well,” Butter told Reuters by email.
“He was not only one of the most positive and happy people I’ve ever met but he made a huge impact on me and how I live my life.
“Then I found out that Kevin has terminal prostate cancer and was given as little as just two years to live. So I wanted to do something to help.”
Despite the obvious challenges associated with endurance running and being away from home for so long, Butter said the biggest test had been the logistical battle.
“The hardest part by far is the logistics of having to travel between countries and sort out visas and paperwork,” he said.
“Emotionally it can be very draining but I am loving every second of it and am meeting some incredible people along the way.”
Butter’s aim is to raise £250,000 ($322,000) for the Prostate Cancer UK charity by the end of his journey in the summer of 2019.