Captain Sir Tom Moore has been hailed as a "hero in the truest sense of the word" and a "beacon of hope for the world" following his death at the age of 100.
The charity fundraiser, who captured the hearts of the nation with his fundraising efforts during the first lockdown, died in Bedford Hospital on Tuesday morning after testing positive for Covid-19.
His daughters Hannah Ingram-Moore and Lucy Teixeira hailed the last year of his life as "nothing short of remarkable", adding: "He was rejuvenated and experienced things he'd only ever dreamed of."
Prime Minister Boris Johnson paid tribute to the veteran, saying: "Captain Sir Tom Moore was a hero in the truest sense of the word.
"In the dark days of the Second World War, he fought for freedom and in the face of this country's deepest post-war crisis, he united us all, he cheered us all up, and he embodied the triumph of the human spirit.
"It is quite astonishing that at the age of 100 he raised more than £32 million for the NHS, and so gave countless others their own chance to thank the extraordinary men and women who have protected us through the pandemic.
"He became not just a national inspiration but a beacon of hope for the world. Our thoughts are with his daughter Hannah and all his family."
Mr Johnson spoke to Ms Ingram-Moore to offer his condolences and the flag above 10 Downing Street will fly at half-mast.
Buckingham Palace said the Queen and the royal family's thoughts are with Sir Tom's family and she is sending a private message of condolence.
Sir Tom had been taken to hospital on Sunday after being treated for pneumonia for some time and testing positive for coronavirus last week.
His family praised the care he had received from the NHS and said they had been able to spend time with him in his final hours.
The Queen is sending a private message of condolence to the family of Captain Sir Tom Moore.
Her Majesty very much enjoyed meeting Captain Sir Tom and his family at Windsor last year. Her thoughts and those of the Royal Family are with them. pic.twitter.com/nl1krvoUlW
— The Royal Family (@RoyalFamily) February 2, 2021
In a statement, Hannah and Lucy said: "We are so grateful that we were with him during the last hours of his life; Hannah, Benjie and Georgia by his bedside and Lucy on FaceTime.
"We spent hours chatting to him, reminiscing about our childhood and our wonderful mother. We shared laughter and tears together.
"The last year of our father's life was nothing short of remarkable. He was rejuvenated and experienced things he'd only ever dreamed of.
"Whilst he'd been in so many hearts for just a short time, he was an incredible father and grandfather, and he will stay alive in our hearts forever."
Singer Michael Ball, who recorded a charity single with Sir Tom that reached number one, said he had spoken to the family and they had told him the veteran "was so proud and so content and he didn't suffer".
While presenting The One Show on the BBC on Tuesday night, Ball said: "What keeps them going, I think, is the outpouring of love and respect for everything that Tom achieved over the last year.
"It has been extraordinary."
Sir Tom's fundraising efforts raised more than £32 million for the NHS, walking 100 laps of his garden before his 100th birthday during the first national lockdown in April.
The veteran set out to raise £1,000 from his charity challenge but his efforts struck a chord with the nation, and praise and donations flooded in.
He raised a total of £32.7 million, with donations from 1.5 million supporters, before his fundraising page was closed at midnight following his 100th birthday on April 30.
Sir Tom started his challenge a little over three weeks earlier, and encouraged people to continue to donate to NHS Charities Together.
In acknowledgement of his efforts, he was knighted by the Queen during a unique open-air ceremony at Windsor Castle in summer 2020.
Sir Tom rounded off 2020 with a trip to Barbados with his family, and his fundraising efforts were marked during the new year drone display in London, as his figure appeared over the O2 Arena.
Ellie Orton, chief executive of NHS Charities Together, said his fundraising efforts had "reached the length and breadth of the UK".
"Captain Sir Tom inspired so many people to take on their own extraordinary challenges, from running marathons to swimming lakes, and he gave us all hope," she said.
"He showed NHS patients and staff who were struggling that people cared, that they were looking out for them and doing what they could to support them.
"Captain Sir Tom was a one-off and he leaves the world a better place."
Landmarks including the London Eye, Wembley Stadium and Blackpool Tower were lit up on Tuesday evening in tribute to Sir Tom.
A picture tweeted from Sir Tom's Twitter account, captioned "Captain Sir Tom Moore 1920-2021", has been liked more than 500,000 times.
Information released on behalf of his family revealed he tested positive for Covid-19 on January 22 after returning home from hospital where he was diagnosed with pneumonia.
A statement said he was tested regularly for Covid-19 between December 9 and January 12 and each test returned negative.
"He was admitted to hospital on January 12. Whilst in hospital he received a pneumonia diagnosis. In addition, as with other patients, he was tested regularly for Covid-19," the statement said.
"On January 22, Tom was discharged from hospital back to the family home where he felt most comfortable. Unfortunately he was left still fighting pneumonia and tested positive for Covid-19 that day.
"He remained at home, cared for by family and medical professionals, until he needed additional help with his breathing. He was taken by ambulance to Bedford Hospital on Sunday January 31."