Labour peer Philip Gould, who was a key strategist and adviser to former prime minister Tony Blair, has died following a battle with cancer, it was announced today.
The 61-year-old died last night at the Royal Marsden Hospital in London with his wife and daughters at his side.
Mr Blair paid tribute to Lord Gould, describing him as an "indispensable" member of the political team which secured three election victories.
He said: "Philip was such a huge part of the renaissance of the Labour Party.
"To me he was my guide and mentor, a wise head, a brilliant mind, and a total rock when a storm was raging.
"He became indispensable. He was always a constant advocate for the British people, their hopes and anxieties. So his political contribution was immense.
"I feel very proud and privileged to have known him and to have been his friend."
Mr Blair added: "But then as his illness gripped him, he became something more.
"In facing death, he grew emotionally and spiritually into this remarkable witness to life's meaning and purpose."
Lord Gould leaves behind his wife, Gail Rebuck and daughters, Georgia and Grace.
Details of a funeral service, to be held in London, are yet to be announced.
Labour leader Ed Miliband said: "Philip Gould was an exceptional man and his death is an exceptional loss.
"He was Labour to his core, and today, as the Labour Party, we mourn for one of our own.
"He was rightly known as a pathbreaking political strategist. His friends will also remember an extraordinary human being - warm, funny, engaging, deeply emotional and loving to all those he knew.
"Nowhere was he more extraordinary than in the final years of his life - battling his cancer like a political campaign that could be mastered and won, then accepting death with courage and bravery.
"His contribution to Labour politics was enormous. His work and commitment helped change the lives of millions of his fellow citizens for the better.
"He taught those fortunate enough to know him much about how to live and, in the years of his illness, much about how to die.
"His memory will live on in his wonderful family and all those who had the privilege to call him their friend."