Who is Bhadrakālī?

The krishna-ekadaśi (11th day of the waning moon) right before Phalahārinī Pūjā is known as the Apara-ekadaśi and it coincides with Bhadrakālī Jayanti, the celebration of Mā in her "auspicious" form. While the word "Bhadra" (which can be both a noun and an adjective) means something like "auspicious", "noble", "protectress" etc. we have to ask: what does that really mean? Is this a gentle (saumya) form of Kālī as contrasted with how She is usually depicted in Her smaśāna/ghora (cremation grou...