New BBC director general Matt Brittin has told staff the BBC "has never been more needed" but that "tough choices are unavoidable as we make savings".
On his first day in the job, the former Google Europe boss said the BBC was the "most trusted news provider, the cornerstone of our creative economy, and a force that brings people together".
But he added that the broadcaster faces "very real challenges", and he must now decide how to make £500m cuts to tackle what the BBC has described as "significant financial pressures".
Brittin has replaced Tim Davie, who resigned last year after criticism that a Panorama documentary misled viewers by editing a speech by US president Donald Trump - who is now suing the corporation.
The BBC has urged a court to dismiss Trump's multi-billion dollar Florida lawsuit, arguing that the Panorama episode never aired in the US.
On Monday morning, Brittin arrived at BBC New Broadcasting House in central London, where he told reporters he was "honoured" and "humbled" to be taking on the role.
He was also greeted by protests from the National Union of Journalists (NUJ), whose members are on strike over shift changes at World Service radio news programmes Newshour and Weekend, and Radio 4's The World Tonight.
Details of further cuts to BBC services are expected in the coming months as the corporation is expected to make to up to 2,000 job cuts to make £500m savings.
In an email to staff, Brittin said: "The BBC has proved throughout its history how quickly it can reinvent itself to serve the needs of audiences - from restructuring for World War II to repurposing during Covid to spinning up services in conflict zones. We need, collectively, to call on that sense of urgency now.
"That means moving with velocity and clarity. Excellence at the BBC has always been founded on great, creative storytelling and brilliant, independent journalism. Today it also means making sure we get the right stories in the right formats on the right platforms.
"We must be where audiences are, and experiment more bravely: test ideas, learn quickly and back what works. Audiences will value the fact we are listening, innovating and working hard to serve them better.
"I know change will not be easy. Tough choices are unavoidable as we make savings. We should ask ourselves, honestly: if we were inventing the BBC today, what would we do? Then respond with clarity, pace and purpose."
The former British Olympic rower worked for Google from 2007 until 2025, serving as the tech giant's head of Europe, Middle East and Africa regions.
Dame Caroline Dinenage, chairwoman of the House of Commons Culture, Media and Sport (CMS) select committee, has said Brittin - whose BBC salary will be £565,000 - "will have a significant job on his hands" in a "period of turbulence" for the BBC.
He arrives following the recent sacking of DJ Scott Mills and a controversy around the broadcasting of a racial slur at this year's Bafta Film Awards.
He must also complete negotiations with the government over the renewal of the BBC's royal charter - which sets out the terms for its existence and funding - which is due to expire in 2027.
In March, the BBC suggested the cost of the TV licence could be cut in return for getting more people to pay the annual charge.
Coming from a "Big Tech" role, Brittin has no prior editorial or programme-making experience, but his job now is to make the BBC fit for the future.
Speaking to Radio 4's Today programme on Monday, award-winning comedy producer Ash Atalla said Brittin has "got a job on" to turn the organisation from "a broadcast-first organisation into a digital organisation".
"I think the time pressure he's under to make that happen is immense," said Atalla.
"The BBC is brilliant at making television shows. I think the BBC has been a little lethargic at making it digital first, then really meeting young audiences, in particular where they are, which is online.
"There's a real clock on it because one of the things that frightens me most of all is when people say, 'We'll miss the BBC when it's gone'. I certainly will and you certainly will, but I'm not sure that our children will, or their children will, because they don't have the nostalgia around the BBC."
Peter Barron, former editor of BBC current affairs TV show Newsnight, worked with Brittin as head of communications at Google and agrees there is a "sense of urgency" for change in "a couple of big areas".
"There's clearly the digital point that Ash makes," Barron said. "I think also public trust is a huge issue.
"There are, unfortunately, swaths of the British population for whom the BBC is no longer for them - both on the left and the right."
He continued: "A lot of young people these days say, 'Well, I don't consume the BBC'.
"Actually, the reality is they do consume the BBC, but maybe they don't realise they're consuming BBC."
