Tributes are being paid to the first Children's Commissioner for Wales, Peter Clarke, who has died, aged 58.
Mr Clarke paved the way as the first UK children's commissioner when he was appointed in March 2001.
First Minister Rhodri Morgan described Mr Clarke as a champion for children who fulfilled his duties with passion, dedication and commitment.
Welsh Secretary Peter Hain said Peter Clarke was "never afraid to stand up and be counted" in his children's role.
Mr Clarke was appointed Wales' children's commissioner on St David's Day in 2001 partly in response to the Waterhouse inquiry into abuse in children's home in north Wales.
During his years in office he spoke out on issues ranging from bullying, to smacking, to the welfare of children in care.
However, Mr Clarke is probably best known for his controversial decision to hold an inquiry into the serial sexual abuse carried out by former drama teacher John Owen on children at a school in Pontypridd .
In a statement, his office said Mr Clarke passed away with his wife Jenny and two sons at his side.
Acting commissioner Maria Battle said: "It will be no surprise to know that, up until the end, his thoughts were of the children and young people of Wales."
An online "remembrance board" is planned by the commissioner's office.
Ms Battle said Mr Clarke had worked "tirelessly to improve the lives of our children and young people".
"We all took strength from the tremendous courage that Peter showed in the face of his illness and from his continued determination to speak up for Wales' children and young people.
"He has inspired his staff to take his vision forward."
Peter Clarke became Wales' children's commissioner in 2001
First Minister Rhodri Morgan said Mr Clarke had "blazed a trail for others to follow".
He said: "He made an enormous contribution to the lives of children and young people in Wales in the past six years and many thousands have benefited, and will benefit in the future, from his work."
Peter Hain said: "It is a credit to Peter's commitment and success that England, Scotland and Northern Ireland have all followed the Welsh lead to establish similar children's commissioner roles."
Children's Minister Jane Hutt appointed Mr Clarke to the commissioner's post and said he became a "a significant and authoritative voice" for children and young people.
Education, Lifelong and Skills Minister Jane Davidson said Mr Clarke "will be an extremely hard act to follow".
She said: "I particularly pay tribute to him for his determination in ensuring that children's voices are heard loudly and clearly by policy makers and that all those of us who hold positions of authority should do all we can to improve services to children, particularly the most vulnerable."
Tributes have also come from opposition parties
Plaid Cymru described Mr Clarke as "a fearless champion of children's rights" who "made a great success of his post".
"He was ready to challenge all the old assumptions and made sure children's voices were heard even when that made difficult hearing for those in power."
For the Liberal Democrats, Peter Black AM said Mr Clarke "was a persistent fighter whose campaigns on behalf of young people have helped to set the agenda in Wales for many years to come".
Welsh Conservatives' health and social services spokesman Jonathan Morgan AM said Mr Clarke "will be a hard act to follow".
"His focus on social care, mental health issues and advocacy gave the assembly the expert and independent viewpoint which we needed," he said.
England's children's commissioner Sir Albert Aynsley-Green also paid tribute to Mr Clarke, saying how he had offered him guidance and support and it was a "privilege to have had the opportunity to work with him".