Former Real IRA leader Michael McKevitt has died following a battle with cancer.
McKevitt, who was one of four men found liable for the Omagh bomb, had been diagnosed with terminal cancer a number of years ago.
He was released from prison in 2016 after serving a 20-year sentence for directing terrorism and membership of an illegal organisation.
The 71-year-old was married to Bernadette Sands McKevitt, a sister of IRA hunger striker Bobby Sands.
From Co Louth, McKevitt always denied being involved in the 1998 Omagh bombing, but in 2009 a judge ruled in a landmark civil trial that McKevitt, Liam Campbell, Colm Murphy and Seamus Daly were all liable for the bomb.
He ordered them to pay a total of £1.6 million damages to 12 relatives who took the case.
A fifth man, Seamus McKenna, was cleared of liability for the bombing.
No-one has ever been convicted of the dissident republican bomb attack in Omagh which killed 29 people, including a woman pregnant with twins.
In a statement issued by Republican Network for Unity on Facebook, they said: "(We) are deeply saddened to learn of the passing of our friend and comrade Michael McKevitt."
In 2019, McKevitt was adjudicated bankrupt in the High Court following failure to pay out the damages.