Widespread tributes have been paid to Norah Gibbons, the first chairperson of Tusla, following her death after a battle with cancer.
Originally a social worker, she would go on to play a key role in a number of inquiries into child abuse and the deaths of children in care.
She was widely regarded as a fearless champion of the rights of children and families.
Her close friend, Adoption Authority chairman Dr Geoffrey Shannon, described her as "a national treasure" who had left "a very significant legacy in the area of child protection".
Children's Rights Alliance chief executive Tanya Ward said she had been one of Ireland's greatest champions of children's rights and social justice.
In a message on social media, her family said she died peacefully at her home on Wednesday evening.
She is survived by her husband Seán and their two children, Myles and Mairéas.
Born Norah Cassidy in 1952 and originally from Boyle, Co Roscommon, Ms Gibbons lived between Clifden, Co Galway, and Clontarf in Dublin.
She graduated with a HDip in Education from NUI Galway in the 1970s and later obtained a masters degree in health and care services from the University of Wales in Cardiff.
Ms Gibbons worked for many years in social work in the UK and Ireland. She joined children's charity Barnardos in the 1990s as a social worker and progressed to a senior management role. Between 2005 and 2012, she was the charity's director of advocacy.
From 2000 to 2009, she was a member of the Ryan Commission, whose report detailed widespread sexual abuse and neglect in institutions for children over several decades.
Ms Gibbons chaired the Roscommon Child Abuse Inquiry from 2009 to 2010, and was involved with Dr Shannon in an independent review of child deaths in 2011 and 2012.
From 2014 to 2018, she served as the first chairperson of Tusla, the child and family agency. She also chaired a Stormont investigation into mother and baby homes and Magdalene laundries, but resigned due to ill health.
More recently, she was appointed by Justice Minister Charlie Flanagan to lead an independent study on familicide and domestic homicide.
Paying tribute to her, Mr Flanagan said: "It was typical of her resolute sense of purpose that, in recent weeks, she was keen to ensure that this important work would be completed and I was glad to be able to give her that assurance.
"Norah was an exceptional woman who brought her innate judgment, common sense and humanity to everything she did."
MEP Frances Fitzgerald, the former minister for children who appointed Ms Gibbons chairperson of Tusla, spoke to her by phone in recent days and said she was "a fighter" who would be sadly missed.
"She didn't bow to authority. She spoke out. She was fearless really," the former minister told the Irish Independent.
"She was very formidable, but also pragmatic and values oriented. She knew what was the right thing to do."
Ms Fitzgerald said Ms Gibbons had "a very wide lens on Irish society", and was committed to righting wrongs, be they in the areas of adoption, historical abuse or vulnerable children.
"She would have had a huge passion for dealing with all of that and was utterly committed to it," said Ms Fitzgerald.
Dr Shannon, who worked with Ms Gibbons on a review into the deaths of 196 children in care, described her as "one of the country's most articulate advocates on the children's rights issue".
He said the phrase "national treasure" was sometimes used inappropriately, but in Ms Gibbons's case it was entirely appropriate.
"We were meeting the most vulnerable citizens in society. Norah had this unique ability to put citizens who are in very difficult times at ease," said Dr Shannon.
In accordance with Government and HSE guidelines and in the interest of public health, a private funeral will take place, followed by cremation.
A memorial service will be held at a later date to celebrate her life.