Former science minister Lord Sainsbury is one of Britain's richest men with a personal fortune of between £1bn and £2bn.
Lord Sainsbury: Well-liked by scientific community
He made his money from the supermarket chain that carries his name - although he now follows its fortunes from the business pages, having given up direct control of his assets when he entered government.
As a junior minister, he has spent the past eight years at the legislative coalface - often working on the unglamorous business of piloting legislation through Parliament.
But the post has allowed him to pursue his passion for science. He has presided over a big increase in government spending in that area and he his known to be well-liked by the scientific community.
Tony Blair has described him as a "great asset" to the nation.
But the peer's other role - as one of the Labour Party's main financial backers - has meant he has also seen his fair share of controversy.
He was recently cleared of breaching the ministerial code in April after failing to disclose a £2m loan to Labour.
He later said he had confused the cash with a declared donation he had made.
Lord Sainsbury was also one of 48 people questioned by police over the cash for honours affair, although he insists this has nothing to with his resignation, as he is not a party fundraiser.
Apart from anything else, he joked: "I have had a peerage for eight or nine years, so there is no question of buying a peerage."
He has stood down, he says, for "personal reasons", although agreeing to carry out a review of science and innovation across government is likely to keep him just as busy as being minister.
The peer is reported to have donated as much as £16m to the Labour Party since Tony Blair became leader in 1994.
In that time, he has helped the party out of many a financial tight spot - including the time he gave £1m to clear its overdraft after the 1997 general election.
But in the 1980s the then plain David Sainsbury began his career as a political donor by bankrolling the Social Democrats. He was a particular admirer of the party's leader Lord Owen.
He switched horses to Labour when it moved toward the political centre following the collapse of the SDP/Liberal alliance.
The peer has also shown his new Labour credentials by financially supporting Progress, the Blairite think tank and magazine.
His financial interest in the development of genetically-modified food has also aroused controversy at a time when the government has come under attack for not banning GM crops.
An invitation to join the government came in July 1998.
Lord Sainsbury accepted and transferred control of his business interests to a blind trust - a standard practice for ministers to prevent any suggestion of a potential conflict of interest.
That portfolio included his holding in Diatech Ltd, the company which owns world-wide patent rights over a key gene used in the process of GM crops.
Even after Lord Sainsbury relinquished direct control of his assets he still managed to be named as the UK company director with the biggest annual equity earnings.
According to Labour Research, the independent research group, Lord Sainsbury earned more than £36m in dividends from his shares in 1998 - more than seven times that of his closest rival.
Lord Sainsbury's interest in science was kindled at Cambridge University in the 1960s. Although initially a history student he transferred to psychology because of a fascination with the breakthroughs then being made in the study of DNA.
The future government minister once said that if a fairy godmother were to grant him a wish it would be to become a Nobel Prize winner in plant genetics.
This passion for genetic research led him to donate £200m of Sainsbury shares to the Gatsby Charitable Foundation which funds work into genetically improving the resistance of plants to disease.