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Australian Tristan Miller (32) came up with the concept after competing in a 90km ultra-marathon in South Africa last year and reading a magazine list of events around the world.
He approached Foss (27), his best friend and then next-door neighbour, suggesting he join him.
"I thought you've got to be joking, I don't run that much, I'm a tennis coach. It's ridiculous," Foss said.
However, he was soon caught up in the "adventure of it" and signed on as Miller's support person - he will get Miller to where he needs to go, film the trip, give massages and fill in if Miller is injured.
"I get to travel the world, see amazing places. It'll be an amazing adventure with my best mate."
He even plans to run some marathons himself, with a goal of completing at least two.
His only run so far has been a half-marathon in Dunedin.
"I've been in training. Five would be an amazing achievement."
Miller, who was made redundant when Google closed its Melbourne office, sold his house to fund the trip, which would involve running marathons in 44 different countries, covering 2100km.
Along the way Foss said he would complete challenges or dares and play a tennis match, with it all appearing on U-tube.
The pair planned to start the trip in Zurich, Switzerland, with a marathon beginning on the stroke of midnight on New Year's Eve.
Next on the itinerary was Israel, Dubai, Canary Islands and Morocco.
"There's one in Rwanda and a reggae marathon in Jamaica."
To make things even more interesting they have planned to run about three back-to-back marathons in different countries, including one in Bordeaux followed by one in Moscow the next day.
While hitting many spots around the world, Miller will not be running in New Zealand but they hope to finish the year with a marathon in Australia, if they can get enough support.
The pair also hope to raise around $100,000 for needy children through Unicef.