Sir Allen McClay died after a short illness
The prominent industrialist and philanthropist Sir Allen McClay, 77, has died in the United States.
He is survived by his wife Heather, who he married in hospital the US in November last year.
Sir Allen, who qualified as a pharmacist in 1953, established his first business, Galen, in 1968.
It became a world-leading pharmaceutical and biotech company and made Sir Allen a multi-millionaire and one of Northern Ireland's richest men.
Tributes have been paid to Sir Allen by the NI deputy first minister, Martin McGuinness, and the chief executive of Almac.
Mr McGuinness said: "I know that I will echo the thoughts of many when I say that we have not only lost a wonderful businessman but also a true gentlemen.
"Sir Allen McClay was perhaps the most successful businessman we have ever produced."
In a statement, Alan Armstrong, Almac CEO said: "Allen was a father figure to every single Almac employee, he often referred to his Almac family and we all shared that view of the organisation he created.
"Our sympathy goes to Allen's family and especially his wife Heather."
Sir Allen established Galen in 1968 and floated the company on the London and Dublin stockmarkets in 1997, establishing the first £1bn company in Northern Ireland and his own personal fortune.
In September 2001, he retired as President of Galen Holdings which later changed its name to Warner Chilcott. However, he soon bought back five divisions and established a new company, Almac.
It became a successful company in its own right, employing thousands of people in the pharmaceutical industry.
Mr McClay was knighted by the Queen in 2005
It is based in Craigavon, County Armagh with other facilities in Scotland, England and the United States.
He was knighted by the Queen in 2005. However he was known to be humble about his success and wealth.
Two years ago, he told The Scientist magazine that "when they say Sir, I look behind me to see who they are talking to".
Last year he redirected a significant slice of his wealth into medical research, setting up the McClay Foundation to unite industry and academia.
The McClay Foundation and Sir Allen became sole shareholders of the Craigavon-based Almac Group, which has a turnover of £167m. It is understood the structure of the foundation will protect Almac from a takeover.
He was one of the largest benefactors of Queen's University in Belfast, personally donating around £20m.
Sir George Bain, a former vice chancellor of the university and a friend of Sir Allen, described him as "a creative entrepreneur in the Ulster tradition of people like Dunlop with tyres and Ferguson with farm machinery."
He said Sir Allen had originally wanted to study English but was encouraged by his mother to take pharmacy as he was more likely to get a job as a result.
Sir George said Sir Allen sometimes described himself as "one of the world's worst pharmacists" and would tell how in his first job with Glaxo he was soon taken out of technical work and put into marketing.
He said Sir Allen was the most significant philanthropist Northern Ireland has ever known.