TV presenter Eamonn Holmes has paid tribute to the bravery of organ donors.
After he broadcast an interview on the subject, Drew Murray, from Antrim, was so moved he donated his kidney to a complete stranger and saved someone's life.
Holmes was asked by Mr Murray to become a patron of the Northern Ireland Kidney Patients' Association.
He said: "How could I say no? Because what I had to do was really very little by comparison to the example that he showed."
The broadcaster is backing a Belfast tree with a connection to the father of medicine to be named Northern Ireland's finest.
It is planted at the Belfast City Hospital and is a direct descendant of the Plane Tree of Kos - under which Hippocrates first taught in 500BC.
It has made it to the final of the Woodland Trust's Northern Ireland Tree of the Year competition.
Mr Holmes added: "To me it represents, I think, our brave organ donors, people like Drew, without whom the work would grind to a halt.
"They go out of their way to give others the gift of life, completely selfless, completely amazing. They are, simply, our heroes."
He said the tree represented hope, humanity, compassion and growth.
"It represents empathy, science, nature and it also represents the future, and that is very, very important in the field of work that we are talking about."
William Johnston was on dialysis for 17 years before receiving a new kidney three years ago.
He said the tree was planted by a student doctor at Queen's who went on to invent an "incredible" dialysis procedure.
"It would be amazing for renal services in Northern Ireland if the tree could win.
"The tree is all about new life and growth, and I would like to think that is what organ donation and transplantation is about, it is about giving new life."