He is the official who will probably have the greatest impact on our everyday lives of any individual policymaker in modern times.
Since the start of the coronavirus crisis, Professor Chris Whitty has been front and centre of the decision-making and communication of messages to the public.
As the government's chief medical adviser, Prof Whitty and his colleagues know their careers will be defined by the UK's response to the pandemic.
Few civil servants in recent British political history can ever have had to carry such a burden.
And few will have had to tell ministers that shutting down a slice of Britons' everyday lives is the only way to stave off the biggest disease threat in living memory.
Who is he?
Prof Whitty actually and confusingly has three titles: the Department of Health and Social Care's chief scientific adviser, chief medical officer (CMO) England and the UK government's chief medical adviser.
His role is to give expert advice to ministers, and his cautious and measured manner is reassuring for someone in that role. Flamboyance and excitable language are not his style.
If not quite a household name, his profile is soaring. Flanked by the government's chief scientific adviser Sir Patrick Vallance, he is becoming an even more familiar figure as daily news conferences on the impact of the coronavirus are staged in Downing Street.
He is even fronting a new government TV advertising campaign to reiterate the message about people keeping themselves and their families safe.
As it happens, Prof Whitty is one of the foremost UK experts in infectious diseases. He is the official in the right place at the right time to be leading Britain's response to the coronavirus.
He played a leading role in the UK effort on Ebola in 2014, when he held the post of chief scientific adviser at the Department for International Development.
Prof Whitty, 53, is a doctor who has practised as a consultant at University College Hospital, London. He was professor of public and international health at the London School of Hygiene and Tropical Medicine.
Whitehall sources say he is a very private person who never discusses his personal life or interests. Scratching his head, one official said: "There was some talk of him enjoying Scottish dancing." He is said by friends to be keen on music and was once a member of a choir.
Prof Whitty only took on the chief CMO role in October 2019, and until the coronavirus threat emerged, he had never done broadcast interviews or held press briefings or conferences.
A Department of Health press adviser took me aside when it was decided he should do his first interview with me in early February.
He asked for an understanding that the CMO might be tentative and nervous about unexpected questions. But from the start he was fluent and clear and not in the least bit flustered.
So how is he regarded by others in the health policy world?
Few doubt that Prof Whitty is a master of his subject. Former health secretary Jeremy Hunt, now chairman of the Commons Health Select Committee, described his as "one of the finest minds I ever worked with and someone who has the great quality he will always tell the truth exactly as he sees it".
Prof Jason Leitch, national clinical director for the Scottish government, says he has worked well in tandem with chief medical officers in Scotland, Wales and Northern Ireland.
"They have spoken often and spoken freely. They have been absolutely together on the difficult decisions based on the science. Chris's scientific evidence-based public health knowledge has been crucial to this," says Prof Leitch.
Some critics have argued that the government's response has been too slow and lagged behind other countries.
They argue that the initial measures were too weak, and much more aggressive social distancing should have been implemented at an earlier stage, following the precedents in Italy and France. There are concerns that the NHS will be overwhelmed without draconian plans to curb the spread of the virus.
Prof Whitty and his colleagues can only tell elected politicians what the science suggests. They must tread a fine line between being seen as spokespeople for the government and speaking truth to power.
Dr Nathalie MacDermott, a clinical lecturer at King's College London, said: 'despite people raising concerns that we are not following the same methods of containment as other countries, I know that Professor Whitty is taking a balanced and measured approach to this situation, which is based on scientific evidence where such evidence is available".
Chris Whitty has certainly not been shy of telling the media what he thinks lies ahead, for example flagging up the possibility of school closures and bans on mass gatherings before any minister or expert had mentioned those options.
But he will have to be judged by how the UK looks in a year's time when, they hope, the peak of the epidemic will have clearly passed and normal life returned.
In the meantime, he will certainly have to prepare the public for some difficult days ahead.