William "Bucky" McCullough (1949 – 16 October 1981) was a Northern Irish loyalist paramilitary with the Ulster Defence Association (UDA). McCullough was a leading member of the UDA's West Belfast Brigade, holding the rank of Lieutenant-Colonel, until 1981 when he was killed by the republican Irish National Liberation Army (INLA).
A native of the Shankill Road area of Belfast, McCullough joined the UDA at its inception in 1971. Within the UDA he garnered an early reputation as a ruthless gunman and was frequently questioned by the Royal Ulster Constabulary (RUC) over his involvement in killings and bomb attacks, albeit without being charged. One of the most notorious incidents that he was held responsible for was a grenade attack on the Gem Bar in the Catholic New Lodge area. He was a close ally of Charles Harding Smith and supported him during the brief period that Smith took the West Belfast brigade out of the mainstream UDA. McCullough was married to Barbara with whom he had six children, the youngest of which, Alan, would also become a leading member of the West Belfast UDA. The couple also had four daughters and another son Kenny.
McCullough was a leading figure within the West Belfast Brigade and was part of the Inner Circle of the brigade, which contained those who were close to Brigadier Tommy Lyttle. McCullough was particularly close to James Craig who was in charge of fundraising for the Brigade and who also maintained a series of shadowy links to some republican figures. In the mid-1970s McCullough was one of four UDA members to accompany Craig to a meeting with five leading members of the Official Irish Republican Army (OIRA) at the Royal Bar, Ann Street in Belfast city centre at which they concluded a series of agreements not to target each other's members and not to get in the way of each other's rackets. All of the republicans present, with whom Craig remained in contact, switched allegiance to the Irish National Liberation Army (INLA) soon after the meeting.