Brian Conlon, founder and chief executive of software and consulting company First Derivatives, has died at the age of 53, the company has said.
The Newry-based company announced in May that Mr Conlon had been diagnosed with cancer.
In a statement, First Derivatives said that he died yesterday.
He is survived by his wife Julie and children.
Brian Conlon founded First Derivatives in 1996 in Newry and had led the company ever since.
The company's clients include JPMorgan, Lloyds Banking Group, Morgan Stanley and UBS.
Non-Executive Chairman Seamus Keating has been appointed Executive Chairman of the company with immediate effect while the process to appoint a new chief executive takes place.
Paying tribute to Mr Conlon, Mr Keating said: "Brian built a world-class business in First Derivatives.
"His drive, ambition and determination inspired all who had the privilege to work with him. This news is a profound shock to all of us," he said.
"We offer Brian's family our sincerest condolences and ask for privacy on their behalf at this sad and most difficult of times."
Mr Conlon worked for KPMG, Morgan Stanley International and SunGard before founding First Derivatives.
The business, which was floated on the stock exchange in 2002, now has more than 2,000 staff and is valed at more than €1bn.
Mr Conlon was also a talented gaelic footballer who represented the Co Down team in the 1980s.
However, his footballing career was cut short due to an injury sustained while playing for Queens University, Belfast in the Sigerson Cup in 1987.
Brian Conlon RIP pic.twitter.com/b7MxI1b3dK
— Official Down GAA (@OfficialDownGAA) July 28, 2019
Down GAA paid tribute to the former player, saying he was a great son of Co Down.
