The First Minister Mark Drakeford and former UK Prime Minister Gordon Brown are among those who have paid tribute to the former Aberavon Labour MP Dr Hywel Francis, who has died.
Dr Francis was elected to represent the Aberavon constituency three times and stood as the town's MP for 14 years from 2001 to 2015.
He had also built a career as a historian.
Paying tribute, First Minister Mark Drakeford said he was honoured to have worked with Hywel Francis.
He said: "It was a privilege to have worked with him, when he ceased to be a member of Parliament and turned his formidable energies to helping the Welsh Government. My thoughts are with Mair and his family.
Gordon Brown, the former UK Labour Prime Minister, shared his condolences in a tweet on Monday morning.
The former UK leader said Dr Francis would be "sorely missed".
He said: "So sorry to hear of Hywel Francis' death: collegiate, friendly, kind and generous, he was a great person to work with. He had a passion for social justice inspired by a very strong sense of history and will be sorely missed. ~GB"
Dr Francis' colleagues from academia also expressed their sadness at the former MP's passing.
Swansea University, where Dr Francis founded the South Wales Miners' Library, said he had made a notable and long-standing contribution to the university and its students.
The Miners' Library Twitter account shared its own tribute, saying: "We are devastated to learn of the passing of Hywel Francis, founder and tireless supporter of the South Wales Miners’ Library.
"His remarkable career as historian, politician and adult educator exuded wisdom, humour and a strong sense of social justice. He will be greatly missed."