Kai hit headlines and prime-time TV news in 2015 after he was abandoned at Ayr train station with nothing but a suitcase full of his belongings.
Thanks to the SSPCA and Mearns animal lover Ian Russell (54) he found happiness in his new East Renfrewshire home.
Now, two years on, Kai is helping the SSPCA by joining Mr Russell on his regular training runs for the marathon, and with his larger-than-life presence will surely help Ian’s bid to boost the charity’s funds.
Ian said: “Raising funds for the Scottish SPCA is what it’s all about. I was lucky enough to rehome Kai and really want to give something back.
“I hand in food and bits and bobs for the animals, and last year I decided to do more for the charity.
“Kai loves coming out running with me when I train and it’s a piece of cake to him as he’s so young and fit.”
He added: “This will be my fourth marathon as I did one when I was in my twenties, and one in my thirties – this is my second time running in London for the Scottish SPCA.
“I’m in my fifties now so training has been more difficult, especially as I’ve had some bother with my ankles, but I’m not chasing a brilliant time,
“I just want to complete it one way or another and support the Scottish SPCA.”
Meanwhile he makes it clear that Kai is his number one inspiration.
He said: “He comes to work with me every day and has a wee face he pulls if he thinks I’m going out without him.
“I’ve always said that it was fate that I was given the opportunity to rehome Kai, although if I hadn’t rehomed him I would definitely have rehomed one of the other dogs in the Society’s care.
“Kai is such a gentle dog and is great with everyone, including children.
“When we’re in the park he usually ends up getting chased by much smaller dogs, ‘though, as he’s just so placid!”
SSPCA Superintendent Sharon Comrie said: “We’re so excited to have Ian representing us at the London Marathon.
“It’s fantastic that he’s decided to take on this huge challenge for us once again and we wish him the best of luck on Sunday.
“Anyone can see that Ian and Kai have a very special bond and we’re delighted this amazing dog has found the true happiness he deserves.”
Anyone wishing to sponsor Ian can visit www.justgiving.com/fundraising/Ian-Russell17 or text KAIX99 followed by their desired amount £1/£3/£5/£10 to 70070