Goll mac Morna

Goll mac Morna (or Goal mac Morn) was a member of the fianna and an uneasy ally of Fionn mac Cumhail in the Fenian Cycle of Irish mythology. He had killed Fionn's father, Cumhal, and taken over the leadership of the fianna, but when Fionn grew up and proved his worth Goll willingly stepped aside in his favour.

His given name was Áed or Aedh mac Morna. He is also known as Áed mac Fidga. He gained the name Goll ("one-eyed") when he lost an eye in his battle with Cumhal or, in other versions, Luchet, as described below:

"Aed was the name of Daire's son,
Until Luchet of fame wounded him;
Since the heavy lance wounded him,
Therefore, he has been called Goll."

When the witch Irnan failed to capture members of the fianna in a magical web, she turned herself into a monster and challenged any one of the finians to single combat. Initially Fionn mac Cumhaill stepped forward but was persuaded by his warband that it would not be heroic for a warrior of his stature to face a hag in combat. Goll took his place and slew Irnan, and was allowed to marry Fionn's daughter as a reward.

In the tale Cath Gabhra, which describes the battle in which the fianna fight and are destroyed by the forces of the High King Cairbre Lifechair, Goll and those loyal to him defect to Cairbre's side and fight against Fionn.

"Tapadh le Goll, mharbh e mhàthair" ("Thanks to Goll, he has killed his mother") was a Gaelic saying used when a nuisance is got rid of by the action of the individual responsible for it. Goll killed his mother by mistake with a bone.

...
Wikipedia