Nobel laureate and Holocaust survivor Elie Wiesel, known as an "extraordinary man" and a "great moral voice of our time", has died.
The death of the 87 year old, whose book Night became a landmark testament to the crimes of the Nazis, was announced on Saturday by Israel's Yad Vashem Holocaust Memorial.
Liberated in 1945 from Buchenwald concentration camp, Mr Wiesel, who lost his parents and a sister in the Holocaust, went on to speak out for victims of violence and oppression.
A staunch humanitarian, when he accepted the Nobel Peace Prize in 1986 he said: "Whenever and wherever human beings endure suffering and humiliation, take sides.
"Neutrality helps the oppressor, never the victim. Silence encourages the tormentor, never the tormented."
Reacting to the news on Saturday US president Barack Obama tweeted: "Elie Wiesel was a great moral voice of our time and a conscience for our world.
"He was also a dear friend. We will miss him deeply."
Former foreign secretary and current president of the International Rescue Committee David Miliband also expressed his sadness at Mr Wiesel's passing.
He tweeted: "Elie Wiesel told me that while the word refugee may not be popular, everyone needs refuge. Extraordinary man, great humanitarian."
Sir Mick Davis, chairman of the Jewish Leadership Council, said Mr Wiesel "dedicated every waking moment" to Holocaust commemoration and to "preserving the of those darkest of times for future generations".
"As burdened as he was with his own suffering and that of all of the victims of the Shoah, he was living proof of the capacity of the human spirit to heal and overcome evil," he said.
"He constantly reminded us that the 'opposite of love is not hate but indifference' and challenged all of humanity to be accountable for their fellow man and to defend the weak and the oppressed.
"Elie called for us never to stand idly by in the face of injustice, for 'neutrality helps the oppressor' and 'silence encourages the tormentor'."
"We have lost a giant amongst men - he will never be forgotten," said Karen Pollock, chief executive of the Holocaust Educational Trust.
"He said, 'Whoever hears from a witness, becomes a witness' - we honour his memory by ensuring that future generations become the witness and carry his legacy."
Mr Wiesel wrote more than 40 books and many essays during his lifetime, lectured around the world and served as a living reminder of the atrocities carried out by the Nazis.
After the war he went to France where he studied literature, philosophy and psychology at the Sorbonne and eventually became a journalist.
In 1956 he was on an assignment to cover the United Nations in New York when he was confined to a wheelchair for a year after being hit by a car.
He ended up staying in New York and in 1963 became an American citizen. He eventually met and married fellow Holocaust survivor Marion Rose and they went on to have a son, Shlomo.
His wife described her husband as "a fighter" in a statement released on Saturday night.
She said: "He fought for the memory of the six million Jews who perished in the Holocaust, and he fought for Israel.
"He waged countless battles for innocent victims regardless of ethnicity or creed."