A professor of mammalian genetics at Cardiff University has been awarded the 2007 Nobel Prize for medicine for his work on stem cells.
Sir Martin Evans with research associate at the School of Bioscience
Sir Martin Evans was honoured along with two US citizens, Mario Capecchi, who was born in Italy, and UK-born Oliver Smithies.
The award recognised the team's work on introducing genetic changes in mice using embryonic stem cells.
Sir Martin described the accolade as like winning the "World Cup".
He said: "It's wonderful - the sort of thing which when you start off as a youngster in science you look up to these fantastic Nobel Prize winners, and think, could that ever be you? No, of course not.
"You can't imagine that these things are going to happen to you and you can't even really honestly even hope for it."
The $1.54m (£755,000) prize is awarded by the Karolinska Institute in Sweden.
Sir Martin, 66, is considered by many the chief architect of stem cell research.
He was knighted in 2003 and received the Lasker award - the American equivalent of the Nobel Prize for medicine - in 2001. He is also a fellow of the Royal Society and fellow of the Academy of Medical Sciences.
The scientist, who graduated from Cambridge in 1963, helped show how the cells that form all the tissues in a mouse's body - embryonic stem cells - can be removed and grown separately in the lab.
He also helped create a method to alter genes in mice with what is said to be amazing accuracy.
Sir Martin is part of a team of three to win the Nobel Prize
This breakthrough, known as gene targeting, is helping the drive to develop new treatments for human illnesses.
Sir Martin said he was driving over to his daughter's house on Monday when he had a call from his secretary in Cardiff telling him to call the chairman of the Nobel committee in Sweden urgently.
He did so and was told he had been awarded the prize.
"I'm so pleased, not only for myself, for all my colleagues who've been involved in this and for the UK too," he said on Monday.
Medicine is traditionally the first of the Nobels awarded each year.
The prizes for achievement in science, literature and peace bearing the name of Alfred Nobel were first awarded in 1901 according to the will of the Swedish dynamite millionaire.
Previously, at least three Nobel laureates have come from Wales but others have lived in the country.
Professor Clive Granger, a statistical analyst from Swansea, was awarded the prize for economics in 2003, while Brian Josephson, from Cardiff, was physics laureate in 1973.
Philosopher and historian Lord Bertrand Russell from Trelleck, Monmouthshire, was awarded the literature prize in 1950.
Dr Robert Huber, who is German, was awarded the 1988 Nobel Prize in chemistry and is currently at Cardiff University.