By Deborah McAleese
Tributes have been paid to the vice-chancellor of Queen's University in Belfast, Professor Patrick Johnston, who has died suddenly.
Mr Johnston, 58, was regarded as one of the world's leading cancer researchers.
The university's registrar, James O'Kane, said his death had caused "a deep sense of shock and loss".
DUP leader Arlene Foster said Professor Johnston was "inspirational in the field of cancer research and was a dynamic Vice Chancellor of Queen's University".
"His loss will be felt not just at home here in Northern Ireland but right around the world where he was hugely respected.
"Myself and many colleagues had the pleasure of working closely with him over the years and we always found him willing to give freely of his time to help make Northern Ireland a better place," Mrs Foster added.
Sinn Fein MLA Mairtin O Muilleoir said Professor Johnston had been "in sparkling form" on Tuesday past as he delivered "a powerful and stirring address to over 100 civic leaders in Belfast City Hall as part of his continuing commitment to leveraging the strength of the university he loved and led on behalf of all the citizens of Belfast".
Mr O Muilleoir added: "His loss will be keenly felt also by all those who admired his determination to find a cure for cancer."
The SDLP's Alasdair McDonnell said Professor Johnston's death was "a terrible loss to Queen's University, cancer research and Northern Ireland".
"Professor Johnston was a powerful figure, working to find a cure for cancer. One of his greatest achievements is undoubtedly leading the establishment of the Centre for Cancer Research and Cell Biology in Belfast," he added.
The UUP's Alan Chambers said: "The entire University community will be feeling (Mr Johnston's) loss at this time and as the university approaches graduations, his absence will certainly be felt by the many students due to pass along the stage to receive their degree certificate."
Professor Johnston was appointed vice-chancellor in March 2014.
Previously he was dean of the school of medicine, dentistry and biomedical sciences at QUB and was regarded as one of the world's leading cancer researchers.
Professor Johnston was also the former director of the Centre for Cancer Research and Cell Biology at QUB.
The 12th vice-chancellor in the university's history, Professor Johnston was married with four sons.