Barrister and political pundit Noel Whelan has died after a short illness.
The 50-year-old former Fianna Fail adviser died on Wednesday evening.
The well-known commentator and father-of-one was instrumental in leading the campaign to introduce same-sex marriage and repealing the Eighth Amendment.
He also founded the Kennedy Summer School, a festival of Irish and American culture in Co Wexford.
He was married to Sinead McSweeney and they have one son, Seamus.
We are devastated and heartbroken to lose Noel so suddenly. It isn't possible to reply to each message right now but know that we are strengthened and sustained by the tributes and kindness. He was our rock and is now our North Star. May he rest in peace.https://t.co/YyjT74NnKg— Sinéad McSweeney (@smcs) July 11, 2019
Irish President Michael D Higgins said Mr Whelan was propelled by his social justice values.
“Noel was not only a commentator but a driving force in some of the most important political campaigns of recent times,” he said.
"Propelled by his social justice values, Noel was not only a commentator but a driving force in some of the most important political campaigns of recent times."— President of Ireland (@PresidentIRL) July 11, 2019
Statement by President Michael D. Higgins on the death of Noel Whelan: https://t.co/4IDH6UBab5 pic.twitter.com/8ZXBqcXMY0
“Ever mindful, and proud, of his roots in Wexford, Noel founded the successful Kennedy Summer School, which continues to make a lasting contribution to our collective understanding of Irish-American history and relations.
“I was delighted to accept his invitation to speak at it last autumn and experienced the warmth and generosity he showed to both speakers and audience, and the ease with which he merged matters of Irish, American and Wexford history.
“He did so by having the significant anniversaries of each of these histories celebrated in a most thoughtful way.”
Fianna Fail leader Micheal Martin described Mr Whelan as a man with “sharp intellect”.
He said: “I was very saddened to hear about the death of Noel, who I have known for many years.
“Noel was a man with a sharp intellect who was born into a Fianna Fail family.
“His father was a Fianna Fail councillor, as is his brother Michael in Co Wexford. Noel was steeped in local, national and international politics from a very young age.
“After college he worked in our party’s headquarters in the early 1990s.
So sad to hear that Noel Whelan has passed away. We come from different party backgrounds but I feel this morning like Ireland has lost a friend. Such a sharp intellect. So articulate and effective on marriage equality.— Leo Varadkar (@LeoVaradkar) July 11, 2019
“From there he learned to be a great political pundit who wrote many books on election results and an extensive book on our party through the decades.
“He understood and knew every constituency and local electoral area across the country and could, of the top of his head, remember quotas from an election held back in the 80s.
“He had a wide circle of friends across the political divide and was very well respected and admired.
“He is a huge loss to everyone in politics but in particular to Sinead and Seamus. Our thoughts are with them at this very sad time.”
Mr Martin, speaking on Today with Sean O'Rourke on RTÉ Radio 1, said Mr Whelan was a person who had "politics in the blood".
"One got a sense of that energy but also someone who always had the next idea in the sense that he was an ideas person.," he said.
"He could read trends very well, how society was moving and changing and the need for organisations like political parties to move like that.
He was a student of history, a barrister and both those combinations are tailor-made for the political world.
Taoiseach Leo Varadkar tweeted: “So sad to hear that Noel Whelan has passed away.
“We come from different party backgrounds but I feel this morning like Ireland has lost a friend. Such a sharp intellect.
Noel changed Ireland for the better
“So articulate and effective on marriage equality.”
Labour Senator Aodhan O Riordain tweeted: “What terrible news. Sympathy to his family and colleagues. What a huge contribution to Irish life.
“Will greatly miss his insights and always remember his role in (marriage referendum).”
Minister for Health Simon Harris said: “Noel changed Ireland for the better. He brought intelligence, fairness and clear thinking to any debate.
“He championed social change and played key role in preparing Ireland to repeal the 8th and introduce marriage equality.”
The Minister for Children and Youth Affairs Katherine Zappone paid tribute to her "very close friend" Noel Whelan as "a man of enormous talent and capacity".
Minister Zappone, speaking on Today with Sean O'Rourke on RTÉ Radio 1, described Mr Whelan as "an incredible strategist and dynamo" who used his campaigning skills to help to win the Marriage Equality referendum.