LONDON (AP) — The rainbow flag flew proudly Thursday above the Bank of England in the heart of London's financial district to commemorate World War II codebreaker Alan Turing, the new face of Britain's 50-pound note.

The design of the bank note was unveiled before it is being formally issued to the public on June 23, Turing's birthday. The 50-pound note is the most valuable denomination in circulation but is little used during everyday transactions, especially during the coronavirus pandemic as digital payments increasingly replaced the use of cash.

The new note, which is laden with high-level security features and is made of longer-lasting polymer, completes the bank's rejig of its paper currencies over the past few years. Turing's image joins that of Winston Churchill on the five-pound note, novelist Jane Austen on the 10-pound note and artist J. M. W. Turner on the 20-pound note.

Turing was selected as the new face of the 50-pound note in 2019 following a public nomination process that garnered around 250,000 votes, partly recognition of the discrimination that he faced as a gay man after the war.

Among his many accomplishments, Turing is most famous for the pivotal role he played in breaking Nazi Germany's Enigma code during World War II. The code had been believed to be unbreakable as the cipher changed continuously. Historians say the cracking of the code may have helped shorten the war by at least two years, potentially saving millions of lives.

“There’s something of the character of a nation in its money, and we are right to consider and celebrate the people on our bank notes," Bank of England Gov. Andrew Bailey said.

“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."

During World War II, Turing worked at the secret Bletchley Park code-breaking center, where he helped crack Enigma by creating the “Turing bombe,” a forerunner of modern computers. He also developed the “Turing Test” to measure artificial intelligence.

After the war, he was prosecuted over his relationship with a man in Manchester and given a choice between imprisonment and probation with the condition of undergoing female hormone treatment, which at the time was used as a form of chemical castration.

His conviction led to the removal of his security clearance and meant he was no longer able to work for Government Communications Headquarters (GCHQ). He died at 41 in 1954 after eating an apple laced with cyanide.

Turing received a posthumous apology from the British government in 2009 and a royal pardon in 2013. Four years later, the Turing law, which pardoned gay men with past convictions, was passed.

Actor and author Stephen Fry said the latest commemoration of Turing marks another step in the nation’s long overdue recognition of “this very great man,” whose “talents ranged far and wide.”

In a YouTube video posted by the bank, Fry laid out the levels of discrimination and “barbaric punishments” that gay men faced in the years after World War II.

“Alan Turing was among the thousands of men who were harried and harangued by the authorities," he said. “Not just down to the hostile attitude to their sexuality alone, but also under the bigoted belief that there was a link between homosexuality and communism."

Over the past decade, Turing's life has become known to a much wider audience, especially in the wake of the 2014 film “The Imitation Game” that saw Benedict Cumberbatch play the role of Turing.

As part of the new note's design — which includes a metallic hologram that changes between the words “Fifty’ and ”Pounds" when the note is tilted and an image of a microchip — the bank collaborated with U.K. intelligence and security agency GCHQ to create The Turing Challenge, a set of 12 puzzles

GCHQ said the full challenge could take an experienced puzzler seven hours to complete and may have even left Turing “scratching his head, although we very much doubt it."

Turing’s great-nephew James Turing, who runs the Turing Trust that refurbishes U.K. computers for use in African schools, told BBC radio that the puzzle is “a wonderful recognition, and a bit reminiscent of the famous crossword that they used for recruiting at Bletchley Park back in the day."