Sir Allen McClay, founder of Almac Sciences and the McClay Foundation, has died in Philadelphia after a short illness. He was 80. The Irish Times has dubbed him “the North’s foremost entrepreneur”, while Martin McGuinness, deputy first minister of Northern Ireland, called him “a wonderful businessman but also a true gentlemen”.

McClay qualified as a pharmacist in 1953 and founded Galen Pharmaceuticals in 1968 and was catapulted into the rich lists when it went public in 1997. In 2001, he retired as president of Galen Holdings after the firm was acquired by Warner Chilcott but returned to buy four former core parts of the company, including the former CSS, which were later renamed the Almac Group.

McClay sunk about £240 million into the new firm, which he initially ran from a Portakabin, saying that he did this because he wanted to look after the “family” of people who had made his fortune. It grew to employ 2,422 people, including 1,559 in the Northern Ireland, offering integrated drug development services to the pharmaceutical and biotechnology industries.

Despite his wealth and being knighted in 2005, McClay avoided the limelight and carried on living in a small house in Cookstown, the town where he was born. His McClay Trust, established in 1998, gave around £20 million to charitable causes, including £10 million to the new Queen’s University Library in Belfast.

This was succeeded last year by the much larger McClay Foundation, which is the sole other shareholder in the Almac Group. The Foundation will continue to use an unspecified proportion of Almac’s profits to advance the use of diagnostic tools and drugs in the prevention, control and cure of disease, especially cancer, to fund research and innovation and to make advances in healthcare available in poorer countries.

McClay is survived by his wife Heather, who he married in hospital the US in November last year, having travelled there for treatment. Philadelphia is also the heart of the Almac Group’s rapidly expanding presence in the US.