In the world of Age of Conan, Morrigan is presumably a Cimmerian goddess. Robert E. Howard makes Conan invoke her in an oath, in The Phoenix on the Sword. "By Badb, Morrigan, Macha and Nemain!" - Conan's actual words - are classified by Howard as "barbaric oaths".
The name Morrigan, especially when connected with the names Badb, Macha, and Nemain, presumably relate to Celtic mythology. There, the Morrigan is a goddess of battle. Morrigan's name means "great queen."
- Conan of the Isles (mention only)