The Ulster Defence Association was formed in 1971 as an umbrella group for a variety of loyalist groups. At its peak it had tens of thousands of members.
The UDA's aims were to protect unionist communities from attacks by republican paramilitaries. At one time, the organisation supported an independent Northern Ireland, but has mostly favoured remaining part of Britain - even threatening to fight the British in order to do so.
It remained a legal organisation until banned in 1991 amid accusations that it was primarily engaged in terrorism. The Ulster Freedom Fighters, who invariably claimed responsibility for acts of terror, is acknowledged to be a cover name for the UDA.
The UDA/UFF is believed to have killed more than 250 people during the Troubles. It has maintained a ceasefire since 1994, with the exception of a series of three reprisal killings for the murder of loyalist leader Billy Wright in 1998.
The UDA's political wing, the Ulster Democratic Party, was dissolved in the early 1990s.