Olly Robbins is never far from Theresa May's side when she travels to Brussels to negotiate Brexit.
He has been the PM's indispensable Europe adviser since she took personal charge of the negotiations over Britain's departure from the EU.
Known by some as the mandarin's mandarin, he is reputed to be the only person in Whitehall to fully grasp the complexities of the British negotiating position.
Officially, Mr Robbins heads the Cabinet Office Europe Unit.
Despite clearly having the confidence of PM, the unelected civil servant is widely distrusted by Brexiteers, who have accused him of trying to engineer the softest possible break with the EU.
And though his mastery of the detail may be unrivalled, some have also questioned whether he has the required experience negotiating in the corridors and backrooms of Brussels.
Mr Robbins originally worked under former Brexit Secretary David Davis in the Department for Exiting the EU.
However, he moved to Downing Street in September 2017.
Some in the Leave camp believe he was the true architect of the doomed Chequers plan, drawn up in the Cabinet Office while Mr Davis and other Brexit ministers were kept in the dark.
Prior to his Brexit role Mr Robbins had a long Civil Service career.
He has worked under every prime minister since Tony Blair, when he served as the Labour leader's principal private secretary.
Aged 43, the Oxford graduate has held senior roles in the Treasury and Home Office and was also deputy national security adviser under David Cameron.
Additional reporting by the Press Association.
