M. Macha Nightmare

M. Macha NightMare (Aline O'Brien) is an American Neopagan witch. She was born in Milford, Connecticut and was one of the founders of the Reclaiming Collective in the 1970s.

In Witching Culture, Sabina Magliocco noted that Nightmare played a key role for several years in the "Spiral Dance", a ritual and dance commemorating the dead performed by Reclaiming for the San Francisco Bay community's Samhain holiday. Nightmare's comments on significant aspects of the emergent Neopagan culture appear throughout Magliocco's book: trance and deity possession, the importance of dance in ritual, rites of passage, design of an initiation ceremony, and the role of folklore in the development of Neopagan consciousness. Jone Salomonsen also cited Nightmare as an authority on Neopagan culture in San Francisco throughout her 2002 book, Enchanted Feminism.

In 2012 NightMare left the Reclaiming Collective, citing that she and the current form of the Reclaiming Collective were incompatible.

NightMare represented Pagans on the Biodiversity Project Spirituality Working Group. She is a member of the American Academy of Religion, Nature Religions Scholars Network, Marin Interfaith Council, United Religions Initiative, Interfaith Center of the Presidio, as well as serving on the Advisory Councils of the Sacred Dying Foundation, and PEARL (Pagan Elders Assistance and Resource League). In 2019 she founded the Earth-based Spirituality Action Team within Citizens' Climate Lobby. In addition, she serves on the Board of Directors of Cherry Hill Seminary.