Denis Martin Donaldson (1950 – 4 April 2006) was a volunteer in the Provisional Irish Republican Army (IRA) and a member of Sinn Féin who was killed following his exposure in December 2005 as an informer in the employ of MI5 and the Special Branch of the Police Service of Northern Ireland (formerly the Royal Ulster Constabulary).

[4] In 1981, he was arrested by French authorities at Orly airport along with fellow IRA volunteer William "Blue" Kelly; the duo were using false passports and Donaldson said that they were returning from a guerrilla training camp in Lebanon.

[5] In the late 1980s, he travelled to Lebanon again and held talks with both Lebanese Shia militias, Hezbollah and Amal, in an effort to secure the freedom of Irish hostage Brian Keenan.

[6] As the Sinn Féin leadership under Gerry Adams and Martin McGuinness turned toward a peace process strategy, Donaldson was dispatched to New York City, where he helped establish Friends of Sinn Féin, an organisation that solicited mainstream political and financial support for the new strategy while attempting to isolate hard-line activists in Irish Northern Aid and other support organisations in the United States.

[12] According to a British agent known as "Martin", prominent South Armagh republicans blamed Donaldson for IRA operations which had been compromised and suspected he had planted covert listening devices which they had found.

[15][further explanation needed] On 19 March 2006, Hugh Jordan, a journalist for the Sunday World, tracked Donaldson down to an isolated pre-Famine cottage near Glenties, County Donegal.

A statement by Northern Ireland Secretary Peter Hain referred to his killing as a "barbaric act", while Taoiseach Bertie Ahern condemned "the brutal murder" of Donaldson.

The Republic's Minister for Justice, Equality and Law Reform Michael McDowell initially said that Donaldson had been shot in the head, and his right hand was also badly damaged by gunshot.

[29][30][31] On 20 September 2016, BBC Northern Ireland's Spotlight aired a programme in which a British spy (known only as "Martin") who had infiltrated the IRA claimed that Thomas “Slab” Murphy and other leading South Armagh Republicans had demanded the killing of Donaldson and that it would have been sanctioned by Gerry Adams.

[32][33][13] On 23 September the solicitor of the Donaldson family after speaking with senior members of the Gardaí said that the allegation was "absolute nonsense" and also that "It does not marry in any way with the lines of inquiry that have been progressed by the Garda or by the police ombudsman.