Independent MP Peter Law died today after a 12-month battle with a brain tumour that nearly forced him to stand down as a candidate for the 2005 General Election.
Mr Law, who leaves a wife and five children, died in the early hours of this morning, his friend Llew Smith said.
The MP, who left the Labour Party after 40 years following a long-running row with the hierarchy over the use of an all-woman shortlist in Blaenau Gwent, won the seat with a huge majority last year.
Mr Law was also the seat's Welsh Assembly member and a former Assembly Government minister.
His departure from Labour last year denied the party its slim governing majority in Cardiff Bay.
Mr Smith, Mr Law's predecessor as Blaenau Gwent's MP, said of his long-time friend: "Peter was a great friend, a comrade and a fine socialist.
"Peter was determined to stand up for the people of Blaenau Gwent and he did that in an amazing way. He was really loved by the people."
He said Mr Law showed particular courage during the last year of his illness.
Mr Law's friend and agent Dai Davies said the 58-year-old had devoted his life to representing the people of Blaenau Gwent for more than 30 years.
Mr Davies said: "First and foremost, my thoughts are with Trish (his wife) and family at this very sad time.
"It's not just a sad time for the family but a sad time for Blaenau Gwent because Peter and the people of Blaenau Gwent were one and the same.
"He has been a true champion of the people and a man of the streets. The pavements of Blaenau Gwent and Peter Law were inextricably linked."
He described his friend of more than 20 years as a "true socialist" who stood up for democracy.
"He lived and breathed electoral politics," he added. "That was his life.
"I don't think, in all honesty, in his life I don't think there was much room for anything more than his family and politics."
Mr Law had three daughters and two sons and had recently become a grandfather, Mr Davies said.
He said the AM and MP continued working throughout his illness.
"Until the last couple of weeks he was in the office. It was only the last few weeks that he became unable to do anything for the constituency."
Plaid Cymru leader Ieuan Wyn Jones AM said Mr Law "was one of the outstanding figures of post-devolution Wales".
"He made a tremendous impact as an Assembly Member and Minister in the National Assembly.
"He was always prepared to speak his mind, and was not afraid to depart from the party line in the interests of his constituents. He was a fluent and convincing speaker. His contributions in the Assembly were often memorable.
"He achieved one of the most remarkable results of the last Westminster election when he stood as an Independent. He felt badly let down by the Labour Party, but the people of Blaenau Gwent repaid his work by electing him with a big majority. He loved the people of Blaenau Gwent and fought unceasingly on their behalf.
"He will be sadly missed in the Assembly. I got to know him well in recent years, and valued his advice on a range of issues.
"He loved the Welsh language and made great efforts to learn it, and served with distinction on the Welsh Language Board.
"My sympathy goes to his family at this sad time. He was a much respected public figure, but also very much a family man."
Plaid's South East Wales AM Jocelyn Davies added that she had "grown very fond of Peter".
"As a Government Minister he treated all Assembly Members fairly.
"He was the people's choice and he represented his constituency to the very best of his ability. He was a good old-fashioned socialist and he will be greatly missed in the Assembly chamber.
"I admired his courage in standing up for what he believed in. Peter was a real character with a smile on his face and a twinkle in his eye."
Conservative Assembly group leader Nick Bourne AM said: "Peter was one of the most principled and courageous people I have ever known.
"He represented the people of his community with honesty and consistency. The last year has called upon his immense reserves of physical and moral courage and he was not found wanting.
"He gained the admiration and respect of people from all political persuasions and none. In all my dealings with him, he was always pleasant, helpful and honest.
"With his passing, political life in Wales is the poorer. I will miss him immensely."
Welsh Secretary Peter Hain said: "Peter Law was a popular politician and I extend my condolences to his family and to his many supporters in Blaenau Gwent.
"Despite his recent estrangement from the Labour Party, which he served for most of his life, Peter still had many friends who will be saddened by his death."
Mr Davies added that Mr Law died in the early hours of the morning, at home and surrounded by his family.
The MP's health had deteriorated over the last two or three weeks, he said.
Islwyn MP Don Touhig, who pleaded with Mr Law not to stand as an independent MP, told BBC's Good Morning Wales that "now is not the time to be talking politics".
"Peter and I may have had our differences but we were still friends. This morning it is time to mourn the passing of a friend," he said.
"People will remember Peter as a hardworking constituency MP. Peter, like me, was very rooted in the valleys and he worked hard for them."
Liberal Democrat Assembly leader Mike German said: "Peter was a dogged fighter to the end.
"He took on the Labour establishment and showed they are not invincible.
"I will remember him for his determination, great warmth and friendliness, which was apparent to all those in his constituency.
"My thoughts are with his family."
Former Welsh Secretary Ron Davies, who counted Mr Law as a personal friend, said: "I feel the deepest sympathy for his wife Trish and his children."
He said Mr Law stood "head and shoulders" above his Assembly colleagues.
"He was personally flamboyant and stood up to speak his mind, which brought him into conflict with New Labour.
"People will remember Peter Law... as a mould-breaker."
He added that the decision by Labour to use an all-woman shortlist in Blaenau Gwent was "like a red rag to a bull".
The Assembly's deputy presiding officer John Marek said: "Peter and I had become very close friends.
"Peter was a great fighter for his constituency, the people of Blaenau Gwent and the people of Wales.
"It's a tragic loss for Wales and he will be very sorely missed."
Bob Crow, general secretary of the Rail Maritime and Transport union, paid tribute to Mr Law, saying: "He was a valued member of our parliamentary group and a tireless campaigner for transport workers.
"He was a principled socialist and his death is a tremendous blow to the Labour movement."
In a statement, First Minister Rhodri Morgan said: "I know I speak for everyone in the Labour movement in expressing my deepest sympathy to Peter's widow and all the family in their bereavement.
"Whatever our political differences over the past year or so, we will always think of Peter's decades of public service to his local community and to the wider Wales, both as a councillor for Blaenau Gwent for over 30 years, as a founder member not only of the National Assembly but also as a founder Labour member of the very first Cabinet of the newly devolved Assembly.
"We will always remember him for his robust and rumbustious contributions to our debates in the Assembly.
"He was armed with a rapier wit but invariably delivered with a smile and without affecting the warmth and camaraderie that underlies all healthy democratic politics.
"It is a great loss for public and political life in Wales that Peter's death has cut short so cruelly his contribution to our civic society."