President Michael D Higgins led tributes for former Labour Party TD, MEP and Senator Brendan Halligan who has passed away aged 84 after a long illness.
Mr Halligan, the founder of the Institute of International and European Affairs (IIEA) died at his home surrounded by his family.
Mr Higgins said that news of Mr Halligan's death "will have been received with great sadness by all those with an interest in politics, economics and social justice".
Taoiseach Micheál Martin described Mr Halligan as "a man who gave his life to politics and the public service with a deep commitment to the institutions of the State".
Labour leader Alan Kelly said he was "a fascinating man with a formidable intellect" as well as "a leading light in the Labour Party".
Mr Halligan trained as an economist, graduating with a master's degree from UCD in 1964. He worked in the public and private sectors as an economist - including in the Irish Sugar Company - before entering politics.
In 1967 he became General Secretary of the Irish Labour Party. While in that post, he was appointed to the Seanad by then-Fine Gael Taoiseach Liam Cosgrave in 1973.
He was elected TD for Dublin South-West in 1976 and became an MEP in 1983. He retired as General Secretary of the Labour Party in 1980 to become an economics lecturer.
Mr Halligan founded the IIEA in 1990 and was its chairperson until 2017. He served as IIEA president until his death.
Mr Higgins recalled how he and Mr Halligan were both senators in the 1970s. He said Mr Halligan "took an early interest, one that never abated, in European affairs".
Mr Higgins also said: "He bore his illness with great courage and patience. Sabina and I send our sincere condolences to his family, and to all those who will have been deeply affected by his passing."
Former Labour Party leader Ruairi Quinn - the IIEA's current chairperson - said Mr Halligan's work to foster greater understanding of European issues in Irish public life was "second to none".
"A convinced European, he profoundly believed that Ireland's interests, and those of its people, were best served at the heart of Europe," he said.
IIEA director general Michael Collins said Mr Halligan's passing was "a great and sad loss to all of us" and expressed "our deepest condolences and sympathy to his wife Margie and to his family."