Known as 'C' due to his habit of initialling papers he had read, Cumming was Chief of the Foreign Section of the Secret Service Bureau - as it was then known - from 1909 until his death in 1923. His influence is still felt today as each subsequent chief of the service has adopted the pseudonym 'C'. That tradition inspired Ian Fleming to name James Bond's fictitious spymaster as 'M'.

With a background in the Royal Navy, Cumming was an inspired choice for the new agency tasked with intelligence gathering overseas. Hard working, committed and secretive he recruited agents to work across the world and was engrossed by what become known as 'tradecraft' - secret writing, disguises, inventions and mechanical gadgets which he trialled in his own lab.

Alex Younger, the Chief of the Secret Intelligence Service, today (Monday 30 March 2015) unveiled the English Heritage blue plaque to Mansfield Cumming at 2 Whitehall Court in Westminster. At various times between 1911 and 1922, flats 53 and 54 - on the building's seventh floor - served not just as Cumming's home, but as the headquarters of the Foreign Section of the Secret Service Bureau. Today the exuberant 19th century French Renaissance style building is grade II* listed, and is now part of The Royal Horseguards Hotel.

During the First World War, Cumming was responsible for creating the wartime network 'La Dame Blanche' - which reported on enemy troop movements, and included 400 agents by 1918 - and aided the arrest of a number of German spies in England.

Vice Admiral Sir Tim Laurence, Chairman of the English Heritage Trust which is responsible for the London Blue Plaques Scheme, said: "Mansfield Cumming was an extraordinary leader whose influence is still keenly felt within MI6 and popular culture today. As the second longest serving Chief, Cumming led the Bureau for 14 successful years, helping to keep Britain safe during one of the most turbulent periods of the twentieth century. It would be difficult to imagine the Secret Service without the legacy of the original 'C'."

Chief of the Secret Intelligence Service, Alex Younger, said: "Although the world in which we operate has changed a great deal since Cumming's day, the values and essential character of the Secret Intelligence Service - the things that make it one of the best human intelligence services in the world - remain strong.

"Cumming might have been surprised at many aspects of our work and lives today - the way in which Britain's role in the world has altered, the way modern technology has developed to sharpen some very human characteristics of our work, and the culture of transparency and oversight in which we now operate for example.

"But I sense he would share the delight I experience today, when I watch a small group of people, embodying the best of modern Britain, penetrate our enemies and disrupt their plans. And doing this, not by force of arms, but by guile, creativity and that thing that he would most certainly recognise: the sheer satisfaction of putting one over on those who mean us harm."

Alan Judd, biographer of Mansfield Cumming, said: "Mansfield Cumming was a retired naval commander of 50 when in 1909 he was offered a second career - to start and run the Secret Service. The organisation he formed grew into what we now know as MI6, shaped to this day by his integrity, determination, humour and idiosyncrasies. Whitehall Court was the Secret Service headquarters and Cumming's home throughout the First World War and it was here that many of the stories, traditions, myths and realities of modern espionage originated."

Cumming becomes the third secret service connection to be honoured with an official London blue plaque, the others commemorate Second World War agents Violette Szabo and F.F.E. Yeo-Thomas GC, 'The White Rabbit'.

The English Heritage London Blue Plaques scheme is generously supported by David Pearl, the Blue Plaques Club, and members of the public.