Morrigan, also known as Morrigu, is the Celtic goddess of war. She is typically depicted as being armoured and armed: wherever war occurs, there is Morrigan. She is reputed to have hovered over the battlefield in the form either of a crow or a raven.
Morrigan has three aspects: Macha, Nemainn and Badb.
The first part of her name is consonant with the Old English maere, part of which still persists within the modern English word "nightmare"; the second part is rigan meaning "queen".
There have been attempts to link the Arthurian witch, Morgana le Fey, with Morrigan. Geoffrey of Monmouth wrote the first stories that describe Morgana le Fey in "Vita Merlini" ("The Life of Merlin,") written during the 12th century. [.. we need to research this fairly thoroughly to disambiguate it... sjc ]