The Gáe Bulg (Old Irish pronunciation: [ɡaːi̯ ˈbulg]) (also Gáe Bulga, Gáe Bolg, Gáe Bolga), meaning "spear of mortal pain/death", "gapped/notched spear", or "belly spear", was the name of the spear of Cú Chulainn in the Ulster Cycle of Irish mythology. It was given to him by his martial arts teacher, the warrior woman Scáthach, and its technique was taught only to him.
It was made from the bone of a sea monster, the Curruid, that had died while fighting another sea monster, the Coinchenn. Although some sources make it out to be simply a particularly deadly spear, others—notably the Book of Leinster—state that it could only be used under very specialized, ritual conditions: