Tributes have been paid to Prof Patrick Johnston, the vice-chancellor of Queen's University in Belfast (QUB), who died suddenly on Sunday.
Prof Johnston's death at 58 had caused "a deep sense of shock and loss", said QUB's registrar, James O'Kane.
Other members of university staff have also expressed their shock.
Senior figures from Northern Ireland's political parties have paid tribute to Prof Johnson, his career and his leading work in cancer research.
His cause of death remains unconfirmed, but BBC News NI's Education correspondent Robbie Meredith understands he suddenly fell ill on Sunday.
World leader in research
Before he took on the vice-chancellorship in 2014, he was dean of the school of medicine, dentistry and biomedical sciences and was regarded as one of the world's leading cancer researchers.
Ulster University vice chancellor Professor Paddy Nixon said he had been shocked and saddened to learn of Prof Johnston's sudden passing.
"My thoughts and sympathies are with his wife and children at this time," he said.
Prof Johnston was the former director of the Centre for Cancer Research and Cell Biology at QUB.
The 12th vice-chancellor in the university's history, he had led the university through a period of change known as Vision 2020.
His priorities in that programme had been to increase the number of international and postgraduate students at QUB and the research income attracted by the university.
He is survived by a wife and four sons.