Former Labour MP and historian Dr Hywel Francis has died, his family has confirmed.
Dr Francis - described as "lovely and compassionate" - was the MP for Aberavon for 14 years until he stood down at the 2015 general election.
He died at Morriston Hospital in Swansea, surrounded by his family.
First Minister Mark Drakeford said Dr Francis proved the "power of solidarity" through his life and work.
UK Labour's Shadow Home Secretary Nick Thomas-Symonds MP said he was "devastated", saying Dr Francis - the son of National Union of Mineworkers' official Dai Francis - "strove to make life better for others".
Mr Drakeford said: "I am deeply saddened to hear of Hywel's passing.
"Hywel's legacy will be forever etched in our nation's story, and his deeply held values shown in his contribution as the Welsh Labour Member of Parliament for Aberavon."
Paying tribute on Twitter, Mr Thomas-Symonds added he was an "all-round lovely, compassionate person".
Devastated to hear the news that Hywel Francis, former @WelshLabour MP for Aberavon (2001-15), historian, activist, and an all-round lovely, compassionate person who strove to make life better for others, passed away earlier today. Thoughts with his wife Mair and all his family.— Nick Thomas-Symonds MP (@NickTorfaen) February 14, 2021
During his time in parliament, Dr Francis served as chair of the Joint Committee on Human Rights, the Welsh Affairs Committee, and two all party groups on archives and history and Down's Syndrome.
Working with the late Lord Jack Ashley, he successfully introduced the Carers Equal Opportunities Act in 2004, which was often referred to as Sam's Bill, in memory of his and wife Mair's son Sam who died in 1997.
It led him to establish and chair the All Party Parliamentary Carers' Group.
Dr Francis's son Dafydd issued a statement, thanking the hospital staff who had cared for his father.
"As a family we want to thank everyone for their messages of condolence," he said.
"We also want to thank all the nurses and doctors at Morriston who looked after my father at such a difficult time for the health service. We have nothing but praise for them."
Mr Drakeford extended "all our thoughts" to "Mair, their family, and friends, at this difficult time."
"[Dr Francis'] books documenting the struggle of Welsh miners against Thatcherism, and their fight against fascism in the Spanish Civil War, stand as monuments to our collective history.
"Through his work and life, he showed how powerful the idea of solidarity can be."
'A brilliant historian'
Shadow Welsh Secretary Nia Griffith MP said Dr Francis "did so much for so many causes" and was a "great friend to many of us".
Labour's Caerphilly MP Wayne David, said: "Devastating news that Hywel Francis has passed away.
"Hywel was a brilliant historian and educationalist."
Neath MP Christina Rees called Dr Francis " a towering figure of our movement", while Rhondda MP Chris Bryant remembered him as "a great campaigner for carers, a splendid historian of the Rhondda, a wise and wonderful man who served Aberavon with all his heart".
Before entering politics, he was a professor of continuing education at Swansea University, aimed at widening community access to learning.
The university tweeted: "He made a long-standing contribution to Swansea University — as an undergraduate, Professor of Continuing Education, and most recently as an honorary fellow.
"We send our condolences to Hywel's family and friends."