Sir Nicholas Winton, who organised the rescue of Jewish children from the Holocaust in 1939, has died aged 106, his family said.
Winton earned himself the label "Britain's Schindler" for saving the lives of 669 children by sending them from Prague to London by train.
His son-in-law Stephen Watson said Sir Nicholas died peacefully in his sleep at Wexham Hospital in Slough.
A statement from the Rotary Club of Maidenhead, of which Sir Nicholas was a member, said: "It is with much sadness I have to report that Sir Nicky Winton died peacefully early this morning.
"Nicky's daughter Barbara and two grandchildren were with him when he died and Barbara said that he was aware of their presence."
It added that he was "probably the oldest active Rotarian in the world".
Sir Nicholas organised eight trains from Prague to London to carry the children away from Nazi-occupied Czechoslovakia when he feared they would be sent to concentration camps.
He also helped to find foster families for the children once they arrived in England, but he did not reveal his astonishing bravery for half a century.
Last year, after being awarded the Order Of The White Lion by Czech president Milos Zeman at a ceremony in Prague, Sir Nicholas thanked the British people for welcoming the children.
"I thank the British people for making room for them, to accept them, and of course the enormous help given by so many of the Czechs who at that time were doing what they could to fight the Germans and to try and get the children out," Sir Nicholas said.
"In that respect, I was of some help and this is the result."
Sir Nicholas, from a German-Jewish family, also received a knighthood in 2003 and a Hero of the Holocaust medal at Downing Street in 2010.
Speaking last year to BBC Radio 4's Today programme, he said he was well aware of the urgency of the situation in 1939.
"I knew better than most, and certainly better than the politicians, what was going on in Germany. We had staying with us people who were refugees from Germany at that time. Some who knew they were in danger of their lives", he said.
On his 105th birthday last year, the founder of the Czech Kindertransport operation was given a cake and card at his home in Maidenhead by newsreader Natasha Kaplinsky, who is a member of the Prime Minister's Holocaust Commission, and visited by Vera Schaufeld, one of the children he saved.
Home Secretary Theresa May, Maidenhead's MP, said Sir Nicholas was a "hero of the 20th century".
She said: "Against the odds, he almost single-handedly rescued hundreds of children, mostly Jewish, from the Nazis – an enduring example of the difference that good people can make even in the darkest of times.
"Because of his modesty, this astonishing contribution only came to light many years later. So many people owe their lives to Nicholas and it was fitting that, in his later years, he finally received the recognition he deserved.
"Maidenhead is rightly proud of all that he did, and we must ensure that his legacy lives on by continuing to tackle anti-Semitism and discrimination wherever it arises."
Chief Rabbi Ephraim Mirvis was among the first to pay tribute to the hero: "Sir Nicholas Winton was one of the greatest people I have ever met - his loss will be deeply felt across the Jewish world."
Prime Minister David Cameron said: "The world has lost a great man. We must never forget Sir Nicholas Winton's humanity in saving so many children from the Holocaust."
Rabbi Lord Jonathan Sacks, who was Chief Rabbi of the United Hebrew Congregations of the Commonwealth from 1991 to 2013, called Sir Nicholas a "giant of moral courage" and "one of the heroes of our time".
He said: "He was 'the British Schindler', all the more impressive for thinking that there was nothing special about what he did, seeking neither honour nor recognition.
"Our sages said that saving a life is like saving a universe. Sir Nicholas saved hundreds of universes. He was a giant of moral courage and determination, and he will be mourned by Jewish people around the world."
World Jewish Relief, a UK-based international Jewish charity, paid its own tribute, saying: "Wishing long life to the family of Sir Nicholas Winton who has passed away at 106. His legacy, saving 669 children from the Nazis, lives on."
Daniel Hannan, MEP for South East England, added: "Of the six-and-a-half million people in my constituency, Nicholas Winton's achievements were the most humbling. RIP."
Michael Zantovsky, Ambassador of the Czech Republic to the United Kingdom, first met Sir Nicholas over 20 years ago and became close friends with him.
He described Sir Nicholas as "a positive man who radiated good".
He said: "I will remember him as one of the most wonderful people I have met in my life.
"In the Jewish tradition he who saves a single life saves the world and Winton saved hundreds of lives.
"It was incredibly moving to be present at some of the gatherings of him with his so-called children and the children of his children. They all owe their existence to him."
He added: "He was always enormously entertaining and he loved life.
"At 106 years old he enjoyed a glass of nice wine and seeing people and having a conversation. That was Nicholas Winton."