The Bank of England has unveiled the new £50 banknote, which celebrates the achievements of mathematician Alan Turing.
Mr Turing helped Britain win World War Two by breaking the German Naval Enigma cipher in 1942 at Bletchley Park – GCHQ’s wartime home.
Sarah John, chief cashier at the Bank of England, told Sky News: "He’s best known for his code-breaking work… but beyond that he’s known as the father of computer science.
"He envisaged the basics of what we’ve come to know as the modern computer and the impact that has had on our everyday lives, that legacy, has been absolutely enormous."
Ms John said the process for deciding who would feature on the note began in 2018 when the Bank asked members of the public for their views.
More than 225,000 names were put forward and Mr Turing was one of 989 individual scientists nominated.
A shortlist of 12 was produced and the Bank’s governor at the time, Mark Carney, chose Mr Turing.
The note features an image of the scientist, mathematical formulae from his 1936 paper laying the groundwork for modern computer science, and technical drawings for the machines used to decipher the Enigma code.
It also features Mr Turing’s words about the rise of machine intelligence: "This is only a foretaste of what is to come, and only the shadow of what is going to be."
The note will be released for public use on 23 June – the day Mr Turing was born in 1912 – and the BoE will give at least six months’ notice ahead of the current notes being withdrawn from circulation.
Security features on the new note include two windows and two-colour foil which, like the £20, are intended to make it difficult to counterfeit.
There is also a hologram image which changes between the words ‘Fifty’ and ‘Pounds’ when tilting the note from side to side.
The Bank’s governor Andrew Bailey said: "There’s something of the character of a nation in its money, and we are right to consider and celebrate the people on our banknotes, so I’m delighted that our new £50 features one of Britain’s most important scientists, Alan Turing.
"Turing is best known for his codebreaking work at Bletchley Park, which helped end the Second World War.
"However in addition he was a leading mathematician, developmental biologist, and a pioneer in the field of computer science. He was also gay, and was treated appallingly as a result."
Mr Turing was convicted of "gross indecency" in 1952 over his relationship with another man, at a time when homosexuality was a crime in Britain.
He was sentenced to 12 months of hormone "therapy" but the conviction also meant he could never again work for GCHQ.
An inquest attributed his 1954 death to suicide.
In 2009, Gordon Brown, who was prime minister at the time, publicly apologised on behalf of the government for Mr Turing’s "utterly unfair" treatment.
Four years later, the Queen granted him a royal pardon.
Mr Bailey said on Thursday: "By placing him on our new polymer £50 banknote, we are celebrating his achievements, and the values he symbolises".
GCHQ has also created its toughest puzzle in honour of Mr Turing being featured on the new banknote, with the organisation’s chief puzzler saying: "It might even have left him scratching his head – although we very much doubt it".
The chief puzzler, identified only as Colin, said: "Alan Turing has inspired many recruits over the years to join GCHQ, eager to use their own problem-solving skills to help to keep the country safe.
"So it seemed only fitting to gather a mix of minds from across our missions to devise a seriously tough puzzle to honour his commemoration on the new £50 note."
Colin said the puzzle will take about seven hours to complete – for an experienced puzzler.
Mr Turing’s great-nephew, James Turing, described the puzzle as a "wonderful tribute and certainly something we’ll be having a go at shortly".
Director of GCHQ Jeremy Fleming said: "Turing was embraced for his brilliance and persecuted for being gay.
"His legacy is a reminder of the value of embracing all aspects of diversity, but also the work we still need to do to become truly inclusive."