Captain David Seath, from Cowdenbeath in Fife, was a fire support team commander in 29 Commando Regiment Royal Artillery.
The 31-year-old suffered a suspected cardiac arrest while running the 26.2-mile course on Sunday. He leaves behind his parents Libby and Pete, brother Gary and girlfriend Gaby Judd.
His mother Libby Seath said: “David has achieved more in 31 years than most people do in 70. He lived his life on the edge and to the full. He was running to raise money for Help For Heroes, a cause which was very important to him.”
London Marathon organisers confirmed he collapsed at the 23-mile mark, receiving “immediate medical attention”, but that he later died in hospital.
Friends and colleagues of the army captain are now vowing to “complete what he started” - finishing the marathon course for him and continuing to raise cash for his chosen charity.
Captain James Walker-McClimens of the 7th Parachute Royal Horse Artillery set up the JustGiving page in his memory.
Having served with Capt Seath in the 19th Regiment The Royal Artillery The Highland Gunners in Tidworth, they then went on tour together to Afghanistan in 2012, returning at the same time.
“We have stayed in touch ever since, he was at my wedding last year,” said Capt Walker-McClimens.
“He was the greatest type of guy you could imagine - everyone loved him. He was funny, outgoing, generous – he was just not a bad guy in any way shape or form.”
Capt Walker-McClimens said those who are finishing the course for him are all fit, but that it is “more fitting” for them to be together when they do it, and will walk the remaining distance instead of running.
So far more than £14,000 has been raised through the JustGiving page set up in his memory – with more than £1,600 pledged to Capt Seath’s original fundraising page.
Capt Seath, who was based in Plymouth, completed two master’s degrees at the University of Aberdeen before joining the Royal Military Academy Sandhurst in 2009.
Lieutenant Colonel Jon Cresswell, Commanding Officer of 29 Commando Regiment Royal Artillery, added: “Dave was an outstanding commando officer, a natural leader and a true gentleman.”