In one version of the myth of the demon Andhaka, Shiva attacked him and every wound he inflicted on the demon created another Andhaka. Shiva and seven other Gods released eight Goddesses who destroyed the demon.
Shiva – Maheshvari, Vishnu – Vaishnavi, Brahma – Brahmani, Karttikeya – Kumari, Indra – Indrani, Yama – Yami, Varaha – Varahi, Narasimha – Narasimhi. (Karttikeya is known as Kumara, hence Kumari.)
The names vary, sometimes seven Matrikas are mentioned.
For the story of Andhaka visit http://sushmajee.com/shiv/legends/1-andhak.htm