Designers and the acclaimed British artist Martin Jennings, who usually works in bronze and stone, have spent more than 18 months on the coin.
On the heads side is the brand new Charles portrait. On the tales side, in tribute to the queen, is the design that first appeared on coins commemorating her coronation at Westminster Abbey in 1953.
“I think it is really poignant that the king’s first coins are in tribute to his late mother,” Rebecca Morgan, director of collector services at the Royal Mint, said.
It takes between 18 months to two years to design a coin, with the monarch personally signing off each one.
Before her death, the queen approved a number of coins — including a Harry Potter commemorative series — and production of those will continue.
Mr Jennings, who usually works in bronze and stone, designed the official portrait of Charles to be struck on to coins.
“It is extremely painstaking work with microns of material,” he said. “It has to be an absolute likeness. It is a portrait of the monarch but also of the individual,” he said.
“It has been a big design challenge. The placing of everything is exactly precise, such as the spacing between the letters, the proximity with the head.
“It is a huge honour. It is extraordinary to think that the smallest piece of work that I have ever done is that one that is going to be reproduced in the most multiples.”
In the portrait, Charles faces to the left, the opposite direction to his mother. This is because tradition states monarchs face the opposite way to their predecessors on coinage.
Tradition also dictates that kings do not wear crowns in their portraits on coins, while queens are pictured crowned.
Mr Jennings worked with images of Charles taken to mark his 70th birthday and began by drawing his design on paper, before creating a model in plaster.
The completed plaster cast was then handed to experts at the Royal Mint, where it was digitally reduced to fit the size of each coin denomination.
Previous works by Mr Jennings include a sculpture of poet Sir John Betjeman at St Pancras Station, one of nurse Mary Seacole by Westminster Bridge and a bronze bust of the Queen Mother at St Paul’s Cathedral.
Workers at the Royal Mint in Llantrisant, south Wales, will produce 9.6 million copies of the coin.
Four presses will be running for 16 hours a day. Each press can strike 400 coins per minute, making around 20,000 coins an hour.
The coins are checked and counted before being packed into cartons of 100,000, which are then sent to banks and sorting offices across the country.
There are approximately 27 billion coins bearing the portrait of the late queen currently in circulation in the UK and they will remain legal tender, being replaced over time as they become damaged or worn and to meet demand.
Historically, it has been common for coins featuring different monarchs to be used at the same time and this will now happen with coins of the late queen and Charles.
Kevin Clancy, director of the Royal Mint Museum, said: “For many people this will be the first time in their lives that they have seen a new monarch appear on money.
“It represents the biggest change to UK coinage since decimalisation and will usher in a new era where the coins of Queen Elizabeth II and Charles co-circulate in the UK.
“The new memorial 50p marks a moment in history and honours a landmark reign that lasted for 70 years.”