Frederick Sanger, the British biochemist who twice won the Nobel Prize, has died at the age of 95.
Fellow researchers have described him as "one of the greatest scientists of any generation" and as "a real hero" of British science.
He is considered the "father of genomics" after pioneering methods to work out the exact sequence of the building blocks of DNA.
Dr Sanger also developed techniques to determine the structure of proteins.
He was born in 1918 in Gloucestershire and initially planned to follow his father into medicine.
However, he followed a career in biochemistry at the University of Cambridge.
He is the only Briton to win two Nobel Prizes and the only scientist to have been awarded the prize for Chemistry twice.
The first came in 1958 for developing techniques to work out the precise chemical structure of proteins.
Proteins are made up of amino-acids. Dr Sanger was able to determine which amino-acids and in what order were used to build the hormone insulin.
He then turned to DNA and its building blocks, bases.
Dr Sanger's group produced the first whole genome sequence, made up of more than 5,000 pairs of bases, in a virus.
He was awarded his second Nobel Prize in 1980 for developing "Sanger sequencing" - a technique which is still used today.
At the time he attributed his success to fellow researchers and his wife: "I was married to Margaret Joan Howe in 1940. Although not a scientist herself she has contributed more to my work than anyone else by providing a peaceful and happy home."
He was awarded one of Britain's highest honours - the Order of Merit - in 1986. However, he declined a knighthood as he did not want to be called a "Sir".
The Wellcome Trust Sanger Institute in Cambridgeshire, which specialises in the understanding of the genome, is named after him.
When the founding director of the institute, John Sulston, asked Dr Sanger if he was comfortable with the site being named after him, the response was: "It had better be good".
He worked until the age of 65 when he retired to spend more time gardening and "messing about in boats".
Dr Jeremy Farrar, director of the Wellcome Trust, said: "I am deeply saddened to learn of the death of Fred Sanger, one of the greatest scientists of any generation and the only Briton to have been honoured with two Nobel Prizes.
"Fred can fairly be called the father of the genomic era. His work laid the foundations of humanity's ability to read and understand the genetic code, which has revolutionised biology and is today contributing to transformative improvements in healthcare."
Prof Colin Blakemore, the former chief executive of the UK Medical Research Council, said: "The death of a great person usually provokes hyperbole, but it is impossible to exaggerate the impact of Fred Sanger's work on modern biomedical science.
"His invention of the two critical technical advances - for sequencing proteins and nucleic acids - opened up the fields of molecular biology, genetics and genomics.
"He remains the only person to have won two Nobel Prizes in Chemistry - recognising his unique contribution to the modern world.
"Yet he was a disarmingly modest man, who once said: 'I was just a chap who messed about in his lab'.
"Fred Sanger was a real hero of 21st Century British science."