It was the largest of the paramilitary organisations, with thousands of members, and was responsible for around 400 murders between 1971 and 2001 as part of its campaign to “protect” unionist communities from the IRA.
Heavily involved in criminality, including the drug trade, it was behind a string of sectarian killings in the name of the Ulster Freedom Fighters (UFF).
These included the Greysteel massacre in 1993 when gunmen entered a pub in Derry and killed eight people.
Notorious former members included Johnny “Mad Dog” Adair, expelled in 2002, the ostentatious Jim “Doris” Gray, shot dead in east Belfast in 2005, and Andre Shoukri, serving a nine-year prison sentence for extortion and blackmail.
The UDA was banned on August 10, 1992.
It was one of several paramilitary groups which took part in a loyalist ceasefire in October 1994. Six weeks earlier the IRA declared its first ceasefire.
In 2000, seven people died after a bloody feud between the UDA and rival loyalist group the Ulster Volunteer Force.
Government recognition for the UDA ceasefire was removed in October 2001 because of the feuding and drug dealing. But in November 2004 former Northern Secretary Paul Murphy said government would again accept the ceasefire following UDA pledges to engage in the peace process.
In 2007, Social Development Minister Margaret Ritchie said she was withdrawing €1.5 million of public money from a UDA-linked conflict transformation scheme in Belfast after the UDA failed to meet a deadline she had set to begin decommissioning.
Her challenge followed serious violence in Carrickfergus, Co Antrim, and Bangor, Co Down, involving police and members of the group.
In November 2007 the UDA issued a Remembrance Day statement in which it said its “war” was over. The following day it said all weapons were being put beyond use but added this did not mean they would be decommissioned.