I think it's about time I dedicate a full post to the subject of the worship of Hekate in ancient Hellas. Most of what a Google search will find on this magnificent Goddess is based upon later sources, or are moderately recent inventions. Note that I have no problem with that: I believe the Theoi can change--especially in the eyes of the people who worship Them--and one of the ways They do so is by the practice of epithets. So, in my personal practice, this dark version of Hekate is an epithet of Her that I respect, but do not offer sacrifice to. It's 'Threefold Hekate': beautiful and powerful in Her own right, but completely unknown to the ancient Hellenes. Yet, even in the time of the ancient Hellenes, Hekate's domains were entirely re-invented, so to say She would not have changed after the fall of the Hellenic empire seems not only futile to me, but disrespectful to a very adaptable Titan Goddess.
Hekate's (Ἑκατη) worship was most likely imported from Thrace or Anatolia, where--especially at the latter--records were found of children being named after Her. This version of Her is single-faced, rules in heaven, on the earth, and in the sea, is a Theia of childbirth--to both animals and humans--and it is She who bestows wealth on mortals, victory, wisdom, good luck to sailors and hunters, and prosperity to youth and to the flocks of cattle. Yet, if mortals do not deserve Her gifts, she can withhold them from them just as easily. After the Titanomachy, Zeus bestowed upon Her the highest of honors. This is the Hekate found in Hesiod's Theogony, written around 700 BC: